An image capturing section captures a face of an observed person. A position detecting section detects, from a face image expressing the face captured by the image capturing section, one of a position expressing a characteristic of a nose and a position expressing a characteristic of a region between eyebrows. A computing section computes a past relative position of a predetermined region of the face that is based on the position detected in the past by the position detecting section. A region position detecting section detects a position of the predetermined region on the basis of the past relative position computed by the computing section and the current position detected by the position detecting section.