PURPOSE: To make the life of a semiconductor laser long and to enhance the operating reliability of a system using it as a light source by a method wherein individual laser resonators are driven respectively independently as currently used ones and as spare ones and, when a currently used laser resonator is deteriorated, it is changed over sequentially to a spare laser resonator.

CONSTITUTION: A drive changeover means 3 drives and stops a currently used laser resonator on the basis of an instruction signal which is output from a deterioration detection means 2. It changes over and drives a spare laser resonator in the remaining part according to the predetermined order of priority. It is used as a new currently used laser resonator. For example, a laser resonator which includes a second stripe region 16 is used as a currently used laser resonator. Concretely, a driving electric-power changeover circuit 3 which supplies electric power to electricity-feeding terminals 18a to 18c as driving parts for individual laser resonators is used, and the supply drive parts are changed over by timing that a deteriorated laser resonator does not radiate a beam. Since spare parts are assembled in a semiconductor laser 1 itself in this manner, the constitution of a device is simplified, and a laser beam can be radiated for a long time and stably.