PROBLEM TO BE SOLVED: To easily achieve temperature control during storage of a breast support table having a built-in X-ray detector of a mammography apparatus.SOLUTION: A thermostat for a mammography apparatus detachably mounted to a breast support table having a built-in X-ray detector of the mammography apparatus for imaging a breast of a subject with an X-ray, includes: a latent heat storage material 13 that shows a phase change at temperatures in a range of 25°C to 33°C and a heater 15 for heating the latent heat storage material.