To obtain a microscope apparatus by which a sample can be observed while a photodecomposable reagent is being decomposed with good efficiency by a method wherein reagent-decomposing light is generated by a nonlinear optical member placed near the sample immediately before the sample is irradiated.

Introduction light is output from a pulse light source 10, and it is condensed in a set direction in a position which is set inside a nonlinear optical member 300 arranged near a sample 900. When the introduction light advances in the member 300, caged reagent-decomposing light is generated by a nonlinear optical phenomenon, and the sample 900 is irradiated. Then, a caged reagent inside the sample in an irradiated position is decomposed, and the amount of a fluorescent substance is increased. In addition, simultaneously with irradiation with the introduction light or after its irradiation, exciting light is output from an exciting light source 120, the sample 900 is irradiated, the fluorescent substance is excited, and fluorescence is generated. The fluorescence is image-formed on a light-receiving face at a photodetector 600 via an observation optical system 500, a sample image is imaged by the photodetector 600, and it is reported to a processing part 700 so as to be processed.