A computer (15) captures the colored moving image of the golfer (11) who swings by gripping a golf club (12) having colored marks (M1 through M3) attached to a shaft (12a) thereof. The computer (15) converts the colored moving image into a plurality of still images; executes binarization for each pixel of a plurality of the still images by using a specific threshold of color information and recognizes pixels, of the still images, which satisfy the threshold as positions of the colored marks (M1 through M3) and extracts a movement of the shaft (12a) by using a movement vector amount of one of the colored marks (M1 through M3 ) or by using a vector angle between two of the colored marks (M1 through M3). In this manner, the computer (15) automatically extracts check-point images.