PURPOSE: To attain two scanning speeds with a simple mechanism by providing a means periodically suppressing the revolving speed of a pinion screw to rotate it at a first slow speed and a means releasing a suppressing means to rotate the pinion screw at a second faster speed.

CONSTITUTION: When a 1 × copying action is instructed, a parent screw 20 is driven by a motor 22, a screw 24 is rotated in the opposite direction to the screw 20, both screws 20, 22 are coupled by the friction of screwing faces, and a carriage 18 is driven at a first slow scanning speed. The motor 22 is reversed, and the carriage 18 is returned to the start point of the scanning position. If the next document is to be copied at a certain shrinkage value, a clutch 50 is released to release a plunger 46 from the exciting position, the screw 24 is freely screwed to a drive screw 20 and is rotated in the opposite direction together with the drive screw 20. When scanning is started, the carriage 18 is driven at a second scanning speed, i.e., a faster scanning speed suitable for the shrinkage mode.