To facilitate deformation of the reflection surface of a reflective member into various shapes, by using a simple mechanism.

A deformable mirror 50 reflecting the illumination light IL includes a mirror element 22 having a reflection surface 22d for reflecting the illumination light IL, a hold block 23A for holding a holding part 22a on the periphery of the mirror element 22, and a plurality of drive units 58 for deforming the reflection surface 22d between a first position and a second position in the direction toward the rear surface 22e of the reflection surface 22d of the mirror element 22, by giving a force toward the rear surface 22e thereto. When the force toward the rear surface 22e is not imparted from the drive unit 58 to the rear surface 22e, the reflection surface 22d is located at the second position.