Light beam cut-off device

A light beam cut-off device comprising:

• a shutter member disposed outside of a light beam scanning device which emits a light beam and between the light beam scanning device and a photosensitive material exposed by a light beam emitted from the light beam scanning device, and supported in a movable manner between a cut-off position at which an optical path of the light beam emitted from the light beam scanning device is cut off by the shutter member, and an open position at which the shutter member retreats from the optical path of the light beam emitted from the light beam scanning device;
• a shutter driving portion for moving the shutter member to the open position at the time the photosensitive material is exposed by the light beam scanning device, and moving the shutter member to the cut-off position at the time exposure for the photosensitive material is stopped;
• and
• a chassis member on which the shutter member and the shutter driving portion are mounted,
• wherein the shutter member is formed into an elongated plate extending in a main scanning direction in which the light beam is deflected by the light beam scanning device, and is supported swingably around a supporting shaft provided at one end thereof in a widthwise direction between the cut-off position and the open position.