A substrate positioning device includes: a supporting unit for supporting a substrate in place; a light emitting unit and a light receiving unit respectively arranged at major surface sides of the substrate to face each other; a light emission control unit configured to control a light emission quantity of the light emitting unit pursuant to a control value; and a detecting unit for detecting a light reception quantity received by the light receiving unit. The substrate positioning device further includes an adjusting unit for controlling the control value pursuant to the light reception quantity while the substrate is not supported by the supporting unit.