A compact laser-scanning microscope that allows in-vivo observation, particularly of cells, with wavelengths ranging from the visible to the infra-red, can be provided. The laser-scanning microscope includes a laser light source unit, an optical fiber, a collimator optical system, an optical scanning unit, a pupil projection optical system, an objective optical system, and a detection optical system that detects fluorescence or reflected light from the specimen, via the objective optical system, the pupil projection optical system, the optical scanning unit, the collimator optical system and the optical fiber. The objective optical system can be attached to and detached from the pupil projection optical system near the intermediate image position.