To provide a plane motor device in which the pitching angle in the movement direction of a slider movable by a plane motor on an X-Y stage is detected, and in which the position error of a load on the slider is eliminated.

The plane motor device is provided with the slider which comprises a light interference part to be position-controlled by the reflected light of a laser beam and a motor to be moved on the X-Y stage, and a control means used to control the movement of the slider. The light interference part is provided with a pitching-direction detection means which receives the reflected light of incident light from at least two laser beam irradiation parts installed in a direction perpendicular to the horizontal direction and which detects its pitching direction.