1. An object detection device for detecting a specific object from an input image, the device comprising: a plurality of classifiers obtained through a learning process using a number of sample images of a predetermined size showing the object, each classifier having assigned thereto a different position on an image to be discriminated and outputting, based on pixel values of pixels at the assigned position, a value representing a probability of the image to be discriminated being an image showing the object; a partial image cutting out device which is a circuitry, or a software recorded on a non-transitory computer readable medium used in a processor, configured to cut out partial images of the predetermined size at different positions on the input image; and a discriminating device which is a circuitry, or a software recorded on a non-transitory computer readable medium used in a processor, configured to sequentially obtain scores of the classifiers in a predetermined order, the discriminating device detecting, for each partial image, a position of a saturated pixel in the partial image, identifying, from the classifiers, a classifier to which the detected position is assigned, obtaining the score of each identified classifier by obtaining a value determined based on a difference between a discontinuing threshold set in advance correspondingly to the identified classifier and a discontinuing threshold set in advance correspondingly to one of the classifiers for which the score is obtained immediately before the identified classifier, and obtaining the score of each of the other classifiers by obtaining an output obtained by applying the classifier to the partial image, each time the score of each classifier has been obtained, determining whether or not a sum of the scores obtained so far exceeds the discontinuing threshold set in advance correspondingly to the classifier, if the sum of the scores obtained so far does not exceed the discontinuing threshold, determining that the partial image is not an image showing the object and discontinuing an operation to obtain the score, if the sum of the scores obtained so far exceeds the discontinuing threshold, obtaining the score of the next classifier, when the scores for all the classifiers have been obtained, determining whether or not a sum of the scores obtained for all the classifiers exceeds a discrimination threshold set in advance, if the sum of the scores obtained for all the classifiers exceeds the discrimination threshold, determining that the partial image is an image showing the object, and if the sum of the scores obtained for all the classifiers does not exceed the discrimination threshold, determining that the partial image is not an image showing the object.