A laser oscillator capable of executing a high-speed feedback control by reducing the control load of a main processor in the feedback control of the laser output. The laser is excited by an excitation source activated by one or more power supplies. The laser radiation is detected by a power sensor or a photodiode. A detected signal is A/D converted and fed to a sub processor or a high-speed DSP. The sub processor compares the current laser output value to a desired control value and calculates a deviation value in a predetermined period. The sub processor outputs a feedback signal to each of the power supplies according to a command from the main processor. Each power supply adjusts the supplied current to control the laser output. The main processor monitors conditions of the power supplies and controls a coolant circulation device. A factor regarding a load on a sequential control process, which may delay the feedback control, is eliminated and an analog circuit is unnecessary. The period time of the feedback control may be within 200 μs.