In a laser beam processing apparatus, a laser monitor comprises a photo sensor, a laser power measuring circuit, an A-D converter, a monitor control unit, a comparison decision unit, a display control unit, a display, an alarm generating circuit and a buzzer. A measured laser power signal (analog voltage signal) representative of an instantaneous value of laser power of a pulsed laser beam is produced by the photo sensor and the laser power measuring circuit, and the digital measured laser power signal from the A-D converter is supplied to the comparison decision unit and to the monitor control unit. The monitor control unit sets or determines a monitor reference waveform corresponding to a laser control reference waveform used for waveform control in the processing apparatus and controls the comparison decision unit. The comparison decision unit provides a monitoring decision on the power of the pulsed laser beam, which is displayed by a visual presentation or by display lamps on the display.