FIG. 4A is a timing chart indicating the vertical synchronization signal (ITOP) 9 and horizontal synchronization signal (HSYNC) 8 generated by the synchronization signal processing unit 18; the image section signal (VE) 7, red component signal 1, green component signal 2, and blue component signal 3 supplied from the host equipment; and the image forming signal (VOUT) 15 supplied from the image pr