1. An image processor, which outputs a result of an estimation of a hidden state of an estimation subject from an observable state in an image in a manner of a time series, wherein: the observable state is observed from the hidden state of the estimation subject under a procedure that has a hierarchical structure, wherein: the hierarchical structure includes: the hidden state of the estimation subject; the observable state; and an intermediate hidden state between the hidden state of the estimation subject and the observable state, wherein the intermediate hidden state has a causal relationship both with the hidden state of the estimation subject and with the observable state; and in the hierarchical structure: the hidden state of the estimation subject has a structure, in which a state transits according to a time change; and the intermediate hidden state also has the structure, in which the state transits according to the time change; and the image processor comprises: at least one camera, with which the image is continuously taken; an estimation part that is configured to process at least the image taken into the image processor and that includes the hierarchical structure; means for producing predictive information of the hidden state of the estimation subject including an accuracy reduction due to disturbance at a present time t, using: estimative information of the hidden state of the estimation subject at a previous time t−1; and a state transition structure of the hidden state of the estimation subject; means for producing predictive information of the intermediate hidden state based on the state transition structure of the hidden state of the estimation subject including the accuracy reduction due to the disturbance at the present time t, using: the predictive information of the hidden state of the estimation subject at the present time t; and the causal relationship between the hidden state of the estimation subject and the intermediate hidden state; means for producing likelihood of the intermediate hidden state including an accuracy reduction due to disturbance at the present time t, using: observed data about the observable state at the present time t; and the predictive information of the intermediate hidden state at the present time t, wherein the structure of the intermediate hidden state, in which the state transits according to the time change, serves as a structure for limiting an accuracy reduction in the predictive information of the intermediate hidden state caused by the accuracy reduction due to the disturbance; means for processing the predictive information; means for producing estimative information of the intermediate hidden state at the present time t, using: the predictive information of the intermediate hidden state at the present time t; and the likelihood of the intermediate hidden state at the present time t; means for producing likelihood of the hidden state of the estimation subject at the present time t, using: the estimative information of the intermediate hidden state at the present time t; and the predictive information of the hidden state of the estimation subject at the present time t; means for producing the estimative information of the hidden state of the estimation subject at the present time t, using: the predictive information of the hidden state of the estimation subject at the present time t; and the likelihood of the hidden state of the estimation subject at the present time t; and means for producing predictive information of the intermediate hidden state based on the state transition structure of the intermediate hidden state including the accuracy reduction due to the disturbance at the present time t, using: the estimative information of the intermediate hidden state at the previous time t−1; and the state transition structure of the intermediate hidden state, wherein: the predictive information of the intermediate hidden state at the present time t, the accuracy reduction of which is minimized, is produced by the processing means as a result of mixing two pieces of the predictive information according to a predetermined mixing ratio, the two pieces of the predictive information including: the predictive information of the intermediate hidden state based on the state transition structure of the hidden state of the estimation subject including the accuracy reduction due to the disturbance at the present time t; and the predictive information of the intermediate hidden state based on the state transition structure of the intermediate hidden state including the accuracy reduction due to the disturbance at the present time t.