A laser processing device having a function for reducing intensity of a reflected laser beam, without stopping laser oscillation, in order to avoid a malfunction due to the reflected beam. A controller for controlling a laser oscillator has: a laser processing commanding part configured to output a laser processing command; a memory configured to store monitored intensity of the reflected beam and a laser output condition; a pre-processing commanding part configured to command a pre-processing prior to the laser processing command; a comparing part configured to compare the stored intensity of the reflected beam to a first judgment value and/or a second judgment value lower than the first judgment value; an output condition changing part configured to set or change the laser output command of the pre-processing command based on a comparison result; and a pre-processing terminating part configured to terminate the pre-processing based on a predetermined condition.