1. A video encoder, comprising: a motion compensation picture signal generator configured to generate a plurality of motion compensation picture signals in accordance with an encoding target signal representing an encoding target picture and a plurality of reference pictures; a prediction signal generator configured to generate a prediction signal of the encoding target signal by utilizing the plurality of motion compensation picture signals; a prediction error signal generator configured to generate a prediction error signal representing a difference between the encoding target signal and the prediction signal; a selector configured to select an entropy code assignment rule that is expected to minimize an information amount of an encoded state of the prediction error signal from among a plurality of entropy code assignment rules for encoding the prediction error signal, in accordance with the plurality of motion compensation picture signals; and an entropy encoder configured to generate encoded information from the prediction error signal in accordance with the entropy code assignment rule selected by the selector.