PURPOSE: To eliminate the high-speed return of lighting devices and prevent heavy shock from being exerted to the lighting devices by opposedly disposing the two lighting devices reciprocatively movably so as to expose and scan the original surface of nearly every half portion of the maximum original length.

CONSTITUTION: Respective lighting devices 12, 13 reciprocatively move while being held in the positions roughly symmetrical to their center CL so as to expose and scan nearly every half portion of the maximum original length. The two devices 12, 13 move at a speed (v) in the direction of going closer to each other from initial positions A, B and reach intermediate positions A1, B1. During this time, lighting light is exposed from the lighting device 12 and a lens 14 moving cooperatively with the device 12 moves from C to C1 at a speed v/2. After stopping for a while, the two lighting devices move at a speed (v) to the direction of the initial positions spacing from each other, and this time the lighting light is exposed from the lighting device 13 and the lens 14 moving cooperatively with device 13 and moves from C1 to C2. The lens 14 resets to the position C and at the time when the device 13 returns to the initial position B, the device 12 returns to the initial position A as well.