A pattern irradiation apparatus includes a light source unit, an objective that irradiates a sample plane with light emitted from the light source unit, a spatial light modulator of a phase modulation type that is arranged at a position conjugate with a pupil position of the objective and that modulates a phase of the light emitted from the light source unit, a light blocking member that is arranged in an optical path between the spatial light modulator and the objective and that is configured to block 0-order light generated by the spatial light modulator, and a control device that makes a correspondence between a focusing position of the 0-order light generated by the spatial light modulator and a position of the light blocking member.