A multi-beam combining apparatus comprising: a phase shifting section, consisting of piezo-mirrors, configured to generate a plurality of phase-shifted laser beams by shifting a phase of each of a plurality of laser beams; a superposing section configured to generate a plurality of superposed laser beams by superposing a reference laser beam and each of the plurality of phase-shifted laser beams; an observing section configured to generate interference pattern data of a spatial interference pattern when observing each of the plurality of superposed laser beams; and a phase control section configured to carry out a feedback control of the phase shift in said phase shifting section based on the interference pattern data obtained from each of the plurality of superposed laser beams, and set each of the plurality of phase-shifted laser beams to a desired state, wherein said observing section comprises a plurality of observing units (81-i) disposed respectively to observe the plurality of superposed laser beams, wherein each of said plurality of observing units (81-i) comprises a plurality of sensors (82-i1, 82-i2) arranged in a repetition direction of the interference pattern and configured to observe an intensity of a corresponding one of the plurality of superposed laser beams in a plurality of observation positions, the repetition direction in which a fluctuation of the intensity of the corresponding one of the plurality of superposed laser beams spatially appears repeatedly, and wherein the interference pattern data contains the intensity observed in each of the plurality of observation positions. a phase shifting section, consisting of piezo-mirrors, configured to generate a plurality of phase-shifted laser beams by shifting a phase of each of a plurality of laser beams; a superposing section configured to generate a plurality of superposed laser beams by superposing a reference laser beam and each of the plurality of phase-shifted laser beams; an observing section configured to generate interference pattern data of a spatial interference pattern when observing each of the plurality of superposed laser beams; and a phase control section configured to carry out a feedback control of the phase shift in said phase shifting section based on the interference pattern data obtained from each of the plurality of superposed laser beams, and set each of the plurality of phase-shifted laser beams to a desired state, wherein said observing section comprises a plurality of observing units (81-i) disposed respectively to observe the plurality of superposed laser beams, wherein each of said plurality of observing units (81-i) comprises a plurality of sensors (82-i1, 82-i2) arranged in a repetition direction of the interference pattern and configured to observe an intensity of a corresponding one of the plurality of superposed laser beams in a plurality of observation positions, the repetition direction in which a fluctuation of the intensity of the corresponding one of the plurality of superposed laser beams spatially appears repeatedly, and wherein the interference pattern data contains the intensity observed in each of the plurality of observation positions.