An optical member and a microscope that allow acquiring brighter and sharper images when fluorescent observation is performed while stimulating a sample with light. Illumination light from a laser unit is split into stimulation light and excitation light by a dichroic mirror. In other words, half of the illumination light is transmitted through the dichroic mirror and becomes the stimulation light, and half of the illumination light is reflected by the dichroic mirror and becomes the excitation light. Half of the excitation light is reflected by a dichroic mirror and is irradiated onto a sample, and half of the stimulation light transmits through the dichroic mirror and is irradiated onto the sample. Fluorescence generated from the sample is totally reflected by the dichroic mirror and the dichroic mirror, and is received by a photodetector.