This optical system (100) comprises a prism (12) and a diffractive optical element (13). The prism (12) has a non-rotationally-symmetric aspheric surface for correcting eccentric aberration, and the diffractive optical element (13) includes a diffractive optical surface (DM) having a lattice structure that is as about an optical axis (Ax) of the optical system (100). The following condition is satisfied where ΔNe represents the refractive index difference of the diffractive optical surface (DM) in relation to the e-line (546.074 nm). 0.53>ΔNe>0.005  (1)