A multi-beam combining apparatus includes a phase shifting section, a superposing section, an observing section and a phase control section. The phase shifting section generates a plurality of phase-shifted laser beams by shifting the phase of each of the plurality of laser beams. The superposing section generates a plurality of superposed laser beam by superposing the reference laser beam and each of the plurality of phase-shifted laser beams. The observing section generates interference pattern data of a spatial interference pattern which appears when observing each of the superposed laser beams. The phase control section carries out a feedback control of the phase shifts in the phase shifting section based on the interference pattern data obtained for every superposed laser beam, and thereby sets the plurality of phase-shifted laser beams to desired states.