To correct positional variation and eccentric error of a light flux by a variable power system in an optical system including the variable power system.

While a second variable power optical system (6) is fixed in a specified variable power state, and a first variable power optical system (4) is changed in two different variable power states; a light flux passing through the second variable power optical system is observed. The positional variation of the light flux is corrected by the first variable power optical system on the basis of the observation result. Next, while the first variable power optical system is fixed in a specified variable power state and the second variable power optical system is changed in two different variable power states, a light flux passing through the second variable power optical system is observed. On the basis of the observation result, the positional variation of the light flux is corrected by the second variable power optical system, and the eccentric error of the light flux is corrected by the first and second variable power optical systems.