To provide a cryostat apparatus for a microscope, which maintains temperature of a sample holder at a prescribed temperature in a range from a cryogen temperature to a room temperature with a minimum evaporation amount of the cryogen without paying attention to pressure of cryogen gas.

A sample holder is heated by a heater and is cooled simultaneously by heat conduction, and temperature control is performed by balancing between heating and cooling. In this case, the degree of thermal coupling of a thermal switch put in a heat conduction path is controlled to reduce heat inflow to a cryogen, whereby the evaporation amount of the cryogen can be minimized.