An optical device comprises a shared phase modulation mask configured to impart a first phase modulation to light of a first wavelength, and imparts a second phase modulation to light of a second wavelength, an irradiation optical system configured to cause the light of the first wavelength and the light of the second wavelength to enter the same incident region in the phase modulation mask, and a light collecting optical system configured to collect the light of the first phase-modulated first wavelength and the light of the second phase-modulated second wavelength to form an image corresponding to a point spread function.