To enable obtainment of a composite image including a movement trajectory of a moving body, even from a moving image including a background. A sampler samples frames from moving image data. A first mask frame calculator calculates mask frames including mask regions, which correspond to positions of the moving body on the frames. A second mask frame calculator accumulates and binarizes the mask frames to calculate a reference mask frame. A region masker masks the frames by using the mask frames and the reference mask frame to cut out moving body regions, which correspond to a moving body, from the frames. A composer overwrites moving body regions on one of the frames in chronological order to obtain a composite image, which includes the movement trajectory of the moving body.