The optical system disclosed in this specification is a variable power optical system for enlarging and projecting a reduction side object onto an enlargement side image plane, or reducing and projecting an enlargement side object onto a reduction side image plane. This variable power optical system includes a first optical component having a reflecting curved surface, and a second optical component disposed more toward the reduction side than the first optical component. The second optical component has a plurality of movable lens units, and the variable power optical system effects a variable power operation by movement of the plurality of lens units. If ray was traced from the reduction side toward the enlargement side, the second optical component forms an image of a reduction side conjugate point on the enlargement side than an optical surface of the first optical component that is most adjacent to the reduction side.