Abstract: A laser exposure apparatus for exposing exposure material (6), such as light-sensitive offset printing plates. The apparatus comprises a relatively heavy base member and an optical scanning unit (2) employing a movable mirror for deflecting a laser beam. The base member (1) comprises a substantially semi-cylindrical exposure surface (5), on which the exposure material (6) can be placed. A bridge (7) is arranged above the base member (1), said bridge being displaceable along the base member in the longitudinal direction thereof by means of an advancing device (8), the mirror being placed on said bridge. The advancing device (8) is arranged along one side of the base member, and the bridge is mounted in a completely or almost completely balanced manner relative to the advancing device (8) by means of a counterweight (9) provided on a projecting portion (7') of the bridge (7), the center of gravity (G) of said counterweight being placed on the other side of the advancing device (8).