Even if an unexpected load is applied to the optical head of an optical printer while the optical head is scanning, an LED and a liquid crystal shutter are driven synchronously with the position of a photosensitive paper to avoid the distortion of the image. A rotary encoder (320) is provided on the rotary shaft of a motor (310) for moving the optical head (100), and the driving timing of the LED (110) and the liquid crystal shutter (150) is synchronized with the output of the rotary encoder.