Diffracted light generated by a diffraction grating passes through a tube lens, reflected by a reflection mirror and forms illuminating light in a strip pattern on the surface of a sample. Thus, fluorescence generated by an objective lens from the sample passes through the objective lens, the reflection mirror and a tube lens, and forms an image of the sample on the diffraction grating. When the diffraction grating is removed from an optical system and a dichroic mirror is arranged, in instead of the reflection mirror, fluorescence from the sample passes through the dichroic mirror, and forms an image of the sample on an imaging surface of an imaging device by an imaging lens. Thus, a microscope which can be used by being switched from a normal fluorescent microscope and uses the diffracted light is provided.