PURPOSE: To provide a highly efficient laser in which the output is stabilized quickly while suppressing the fluctuation without additionally inserting an optical element, causing increase of reflection loss, into an optical resonator.

CONSTITUTION: The solid state laser for pumping a semiconductor laser comprises a function for controlling the temperature of a solid state laser crystal 7, a thermister 16 for measuring the temperature in a laser head part 1, and a function for controlling the ambient temperature of a nonlinear optical crystal 11 in relation to the temperature in the laser head part 1. The function for controlling the ambient temperature of the nonlinear optical crystal 11 is achieved by a bridge circuit or a CPU.