Patent ID: 8300074

Claim:
An exposing device comprising; a plurality of exposing units which forms a latent image, wherein each of the plurality of exposing units includes: an exposure light source; a rotating polyhedron that reflects light from the exposure light source to exposedly scan a photoconductor with the reflected light while rotating; 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, the light being reflected by the rotating polyhedron; 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; and a phase difference detecting unit that determines whether a phase difference between the detection signal of the second detecting unit of each of the exposing units is less than a predetermined phase difference when the first control is switched over to the second control by the control unit of the exposing unit.