PURPOSE: To provide a glass layer thickness correcting device for a microscope capable of achieving the performance of a microscope to the maximum by correcting the dispersion of the thickness of a glass layer lying between a sample and an objective lens.

CONSTITUTION: This device is provided with a fixed window 18 having a window part 18a perpendicular to an optical axis 22 on the optical axis 22 under the objective lens 13, and a movable window 19 having a window part 19a parallel with the window part 18a of the fixed window 18 on the optical axis 22 under the fixed window 18. A space 24 between the windows 18 and 19 is filled with light transmissive liquid having a refractive index equal to glass constituting the windows 18 and 19. Then, the window 19 is freely moved in an up-and-down direction by a window driving mechanism 21 in a state where the space 24 is filled with the liquid 20.