An exposing device includes a plurality of exposing units which forms a latent image, wherein exposing units includes: an exposure light source; a rotating polyhedron that reflects light from the exposure light source; a driving source that rotates the rotating polyhedron; a first detecting unit that detects the number of rotations of the driving source; a second detecting unit that detects the light from the exposure light source at a position; and a control unit that performs a first control of the driving source based on a detection signal of the first detecting unit at a start of the rotation of the rotating polyhedron and thereafter performs a second control of the driving source based on a detection signal of the second detecting unit.