Problem: To provide an observation auxiliary device that can appropriately and readily perform observation using an exciting light as a light source.Resolution Means: Provided are an imaging unit 104 that uses a light emitted from a second beam splitter 202 of a microscope 2 that can use an exciting light and an observation light, which is a light including a wavelength other than that of the exciting light, as a light source by switching there between and is provided with the second beam splitter 202 to image images of the same observation region of the microscope 2 in situations where the exciting light and the observation light are used as the light source and an output unit 106 that overlaps, synthesizes, and outputs the images imaged by the imaging unit 104 respectively using the exciting light and the observation light as the light source.