PURPOSE: To facilitate operation for dismounting a photosensitive plate and to enhance operation efficiency, by moving a photosensitive plate holder automatically from a printing position to this side by a specified mechanism, turning it inside out, and returning again to the printing position.

CONSTITUTION: A photosensitive plate holder 14 is provided slidably forward and backward with a motor 31 by engaging the female screws guide rods 18A, 18B fixed to a support shaft 15 with male feed screws 19, and the holder 14 is turned with a motor 36 by engaging the gear 35 with a worm gear 38. When printing is finished, the holder 14 is unlocked, the motor 31 is actuated to move it to this side, the motor 36 is actuated to turn it inside out and to return it again to the printing position, and it is locked. These sequential operations are conducted automatically through a specified limit switch 41, etc. Before the next printing, the photosensitive plate is exchanged for a new one in this side, thus permitting mounting and dismounting operations to be made easy and operation efficiency to be enhanced.