When frame data is acquired to a digital camera, a block split section splits the frame data into a plurality of correlation detection blocks, an average value calculation section calculates an average pixel value of each of the correlation detection blocks, and an activity calculation section calculates a block activity value of each of the correlation detection blocks from the calculated average pixel value of each of the correlation detection blocks. Next, a group allocation section allocates the individual correlation detection blocks to two groups on the basis of the calculated block activity value, and a motion vector for each group is calculated using the representative point matching method. Next, the motion vector calculation section calculates the entire motion vector from the motion vectors for each group in accordance with the ratio between the numbers of calculation detection blocks in each group.