PURPOSE: To control a variation in a spot diameter and a spreading angle of a laser beam by disposing an n-type semiconductor on a surface of a p-type clad layer except a reflecting mirror, and applying a reverse bias voltage to a junction surface between the clad layer and the semiconductor.

CONSTITUTION: A laser is formed in shape in which both sides of a p-type clad layer 53 are held by n-type semiconductors 51. A central electrode 100 is for oscillating a laser, and both side electrodes 200, 300 are for varying the magnitude of a laser emitting pot. A potential higher than that of the electrode 100 is applied to the electrodes 200, 300. Thus, a current flows from the electrode 100 to a lower electrode, and the center of an active layer 54 emits a light. On the other hand, a depleted layer 80 is formed in a p-n junction between the layers 51 and 53. A reverse bias voltage to be applied to the junction is varied by altering a power source potential to vary spreading of the layer 80. If the layer 80 is small, the flowing width of the current is increased, and the spot is increased. If the layer 80 is large, the spot is decreased.