With the object of preventing deterioration of or damage to a photodetector caused by excessive light by more reliably preventing the excessive light from entering the photodetector, a microscope of the present invention is provided with a high-sensitivity detector, such as an HPD, a GaAsP, an EM-CCD or the like, that detects observation light coming from a specimen, a box-shaped casing that has an opening that allows contained items to be placed therein and removed therefrom and that covers the high-sensitivity detector, a door that can close off the opening of the casing, a switch that restricts light detection by the high-sensitivity detector by turning on and off a drive voltage to be applied to the high-sensitivity detector, and an opening restricting mechanism that allows the opening of the casing in the closed state imposed by the door to be opened only when the light detection by the high-sensitivity detector is restricted by the switch.