A generation unit generates N distortion corrected images (N≥2) by performing coordinate conversion on each of N partial areas of a first captured image, using a conversion parameter that depends on a position of the partial area, and generates N distortion corrected images by performing coordinate conversion on each of corresponding N partial areas of a second captured image, using a conversion parameter that depends on a position of the partial area. A detection unit detects N motion vectors by comparing each of the N distortion corrected images generated from the first captured image with the corresponding distortion corrected image generated from the second captured image. A conversion unit generates N converted motion vectors by performing inverse coordinate conversion on each of the N motion vectors using a conversion parameter that depends on a position of the corresponding partial area.