An overall motion detecting device (1) includes a search region variable-shaped motion detector (2) and an overall motion information generator (3). The overall motion information generator (3) controls a surveillance camera (5) which is an external image capturing system and supplies control information of the surveillance camera (5) (such as moving direction, angular speed and focal length) to the search region variable-shaped motion detector (2) as overall motion information (S3). The search region variable-shaped motion detector (2) calculates a motion vector (mv) while renewing, by picture, a search region having a search shape determined by the overall motion information (S3) and a region area suitable for its operational capability.