A laser diode pumped solid state laser is provided with a first temperature control circuit which controls the temperature of the laser diode to a predetermined value and a second temperature control circuit which controls the temperature of the resonator of the solid state laser to a predetermined value. When the solid state laser is in a steady state, an automatic power control is carried out for keeping the light output of the solid state laser at a reference output value. When a predetermined command is issued, the automatic power control is switched to an automatic current control for keeping the electric current flowing through the laser diode at a reference current value. A temperature of the laser diode at which the light output of the solid state laser is maximized is detected while changing the temperature of the laser diode, and the first temperature control circuit controls the temperature of the laser diode to the detected temperature. A temperature of the resonator at which the light output of the solid state laser is maximized is detected while changing the temperature of the resonator, and the second temperature control circuit controls the temperature of the resonator to the detected temperature.