A mounting section (2) for a user to mount on his/her head includes an infrared light irradiation section (5) that irradiates an object to be detected (21) with a predetermined pattern of infrared light and an infrared light detection section (6) that detects the infrared light reflected by the object to be detected (21). The infrared light irradiation section (5) and the infrared light detection section (6) are placed at a predetermined distance from each other. The three-dimensional coordinates of the object to be detected (21) are computed from a predetermined pattern of reflection from the object to be detected (21) as obtained by the infrared light detection section (6).