PURPOSE: To control laser outputs, motor revolutions and the synchronization of beam modulation by detecting the transmitted and reflected rays from the patterns recorded between the respective holograms of a hologram scanner wherein plural holograms are arrayed in the rotating direction.

CONSTITUTION: A glass disc 21 is recorded with many holograms 211, 212,...22n at constant intervals on the same circumference, and is recorded with prescribed patterns 231,...23n between the respective holograms. Each of the holograms corresponds to one surface of a polygonal mirror, and deflects each laser beam by each one time. A semiconductor laser 24 is driven by a driving circuit 26 according to the information signal from a modulating circuit 25. When the laser beam is transmitted through the patterns provided between the holograms, it is made incident to a photodetector 30 in a non-modulated state. The output from the photodetector 30 is used commonly for the speed control of a DC motor driving a light deflector, the control of the laser output and the control of synchronization.