A variable power relay optical system is arranged closer to an image side than an imaging optical system. The variable power relay optical system includes, in order from a side of the imaging optical system, a front group that is arranged between the imaging optical system and a position of an image of a sample that is formed by the imaging optical system, the front group forming an intermediate image formed by reducing the image, and a rear group that forms a relay image formed by magnifying the intermediate image, the rear group including a plurality of lens groups that each move along an optical axis so as to change magnification of the rear group without changing a distance from the front group to the relay image.