An optical apparatus is disclosed, which is suitable for the focus detection by the TTL phase difference detection method, and capable of producing a pair of phase difference images for focus detection with high accuracy. The optical apparatus comprises a deflection optical element which deflects at least one of first and second luminous fluxes with respect to the other. The first and second luminous fluxes are transmitted respectively through first and second areas of an exit pupil of an optical system, and then reach a photoelectric conversion element. The deflection direction of the luminous flux is different from the division direction of the first and second areas.