A motion picture encoding method includes searching for a first motion vector between an object block of an input motion picture and a reference image for a frame-based prediction mode, searching for a second motion vector between the object block and the reference image for a field-based prediction mode, generating a first and second predictive residuals in accordance with the first and second motion vector, extracting a first and second feature quantities indicating a first and second similarity between lines of the first and second predictive residual, selecting the frame-based prediction mode in a case where the first similarity is larger than the second similarity based on the first and the second feature quantity, selecting the field-based prediction mode in a case where the second similarity is larger than the first similarity, and inter-frame-coding the input motion picture in accordance with the selected prediction mode.