Abstract: In a solid-state laser device comprising a slab-shaped laser medium, first through n-th excitation units are arranged on the slab-shaped laser medium to define first through n-th partial zones and to generate first through n-th laser beams from the first through n-th partial zones along optical axes, respectively. In order to selectively energize the first through n-th excitation units, a reference light beam is previously generated by a beam generator to be delivered through a fixed mirror and a beam distributor to a selected one of the first through n-th partial zones. Thereafter, the reference light beam travels through the slected partial zone to be received by a photosensor. The photosensor detects the selected partial zone to energize a selected one of the first through n-th excitation units that is made to correspond to the selected partial zone.