Two light-emitting units are to be prevented from overlapping each other in an image obtained through a camera. A tracked unit (30) has a first outer surface (A1) provided with a first light-emitting unit (H1), a second outer surface (A2) provided with a second light-emitting unit (H2), and a light shield portion (B). The second outer surface (A2) faces a second direction different from that of the first outer surface (A1). The light shield portion (B) is located further outside than the first light-emitting unit (H1) and the second light-emitting unit (H2).