A zooming optical system has at least one lens unit having a variable magnification function and at least one deformable reflecting surface having a compensator or focusing function. In this case, the zooming optical system satisfies the following conditions: 0|x/|0.5, 0|y/|0.5, where x is power of an axis perpendicular to a direction of decentering of the deformable reflecting surface; y is power of an axis in parallel with a direction of decentering of the deformable reflecting surface; and is power of the entire optical system.