A laser apparatus comprises storage means for storing a power source voltage of each pulse at the time of continuous pulse oscillation for one cycle, with each voltage correlated with an identifier which specifies the respective pulse, and output control means for, when a pulse is generated, reading from the storage means the source voltage of a pulse having the same identifier, and performing pulse oscillation on the basis of the source voltage. Thus the influence of the spiking phenomenon during a burst mode operation is eliminated as much as possible, and thereby the accuracy of laser beam machining is still more improved.