A frame storage stores an image obtained by imaging a region of at least part of the body of a user. A vital sign signal detector detects a signal sequence of a vital sign that cyclically varies from plural imaged regions of the body of the user by using captured images of a predetermined number of frames stored in the frame storage. A correlation calculator obtains the correlation between the signal sequences of the vital sign detected from the respective imaged regions of the body. An identity determining section determines whether or not the respective imaged regions of the body belong to the same user based on the correlation between the signal sequences of the vital sign detected from the respective imaged regions of the body.
