A microscope apparatus includes a laser beam source for emitting a laser beam, an objective lens for irradiating a sample with the laser beam, a phase-modulating spatial light modulator placed between the laser beam source and the objective lens at a position optically conjugate with a pupil position of the objective lens, and a beam diameter variable unit placed between the laser beam source and the phase-modulating spatial light modulator for varying a beam diameter of the laser beam incident to the phase-modulating spatial light modulator.