PURPOSE: To record an image without delay in a main scanning direction by early rising an image forming signal for a delaying time of a semiconductor laser for the forming signal.

CONSTITUTION: A laser light is guided to an optical fiber 7 by a BD (beam detecting) mirror 6 at each one main scanning, and sent to a BD processor. An image forming position of the light is determined with the BD signal formed by the processor as a reference. For example, the position of the mirror 6 for obtaining the BD signal is deviated and set to a position for detecting the light as early as 120nsec, and sending of the forming signal is started after a predetermined time t1 to be determined in advance by an interface circuit, etc. On the other hand, since a laser output is delayed at the time t1, the start timings of the BD signal and image forming after delaying can be maintained just in a desirable phase relationship by delaying the BD signal at t2=120 -td.