A plasma is excited uniformly as a whole over the length of each slot. A laser oscillating apparatus is designed to excite a laser gas in a laser tube (2) by introducing electromagnetic waves into the laser tube through a plurality of slots (10) formed in a waveguide wall and generate a laser beam by resonating the light generated from the laser gas. A least one electrode (13) is placed near the slot (10). By giving a predetermined current density to the electrode (13), the intensity distribution of light generated from the laser gas above the slot (10) is controlled. <IMAGE>
