An isolated light-shielding pattern formed from a light-shielding film region 101 and a phase shift region 102 is formed on a transparent substrate 100 serving as a mask. By transmitting a second frame that repeats the truncation of the TXOP transmitted from the first station, a hidden node problem can be avoided and equitable access to the medium provided by ensuring that stations that may be outside the broadcast range of the first station also receive the frame truncating the TXOP. The end point of a given user epid can be uniquely identified by creating a key from an epid and a user’s address-of-record. The absolute position of the target object point is derived on the basis of the results of the bundle adjustment and the absolute positions of the camera represented by the position data.