An optical system 10 includes a front group 11, a light shielding member 4, and a rear group 12 disposed in order from a side of an object to a side of an image. The light shielding member 4 has an opening. The rear group 12 has a diffraction surface 5 and an aspherical surface 6. The aspherical surface 6 in a first section has a non-circular-arc shape. The grating spacing of the diffraction surface 5 in the first section changes from a center portion toward a peripheral portion to include an extremum value at the center portion. In the first section, the shape of at least one of a base surface of the diffraction surface 5 and an optical surface disposed closer than the diffraction surface 5 to the side of the object is asymmetric with respect to a normal line at a vertex thereof.