There is disclosed a laser scanning microscope including a first optical scanning system which scans a first laser light for observing a sample on the sample, a first light branch device which branches the light from the sample from an optical path of the first laser light, a photodetector which detects the light from the sample, separated by the first light branch device, a second optical scanning system which irradiates a specific portion on the sample with a second laser light for stimulating or operating the sample, and a wavelength selection device which is disposed between the first light branch device and photodetector and which includes a first function of transmitting a desired observation light and a second function of limiting transmission of the second laser light.