Interference observation device and interference observation method

An interference observation device, comprising:

• a light source that outputs light;
• an interference optical system that includes a reference mirror, splits the light output from the light source into a first light and a second light, and outputs interference light between the first light reflected by an observation object and the second light reflected by the reference mirror;
• an image sensor that detects the interference light;
• and
• a processing unit that acquires an interference image based on a detection result of the image sensor,
• wherein the interference optical system includes a mechanism configured to change a focal condition of an optical path of the second light, and
• the processing unit separates observation surface information related to an observation surface of the observation object and non-observation surface information related to a non-observation surface other than the observation surface, based on a plurality of the interference images obtained when the focal condition of the optical path of the second light is changed in a state in which a focal point of the first light is aligned with the observation surface.