Dot width data of a plurality patterns each corresponding to a recording range in one scanning operation are stored in a memory in advance. Each dot width data required to correct an f-.theta. error is used to determine each dot width in one scanning operation. In accordance with the operation of an address counter, a bus switching circuit selectively reads out dot width data of a pattern different from a preceding pattern from the memory for each scanning operation, and outputs the data to a latch circuit. A programmable counter determines each dot width of image data on the basis of the dot width data from the latch circuit. A laser diode driver ON/OFF-controls a laser beam from a laser diode on the basis of the image data from the programmable counter.