A foreign substance detection system, provided close to a planner light-transmissive plane member, to detect substances present on the planner light-transmissive plane member,
- the foreign substance detection system comprising:
- a light emitting member to emit light toward the inner surface of the planner light-transmissive member;
- an optical device, having an input surface through which a part of the light emitted from the light emitting element enters the optical device and a transparent face, provided in close contact with the inner surface of the planner light-transmissive member, to transmit a light reflected from an outer non-substance detected area where a substance is not present on an outer surface of the planner light-transmissive member;
- a light-guiding member to guide another part of the light that does not pass through the input surface of the optical device toward the planner light-transmissive member, the guided light being to be reflected from an inner substance detected area where a substance is present on the inner surface of the planner light-transmissive member;
- a first light receiving member to receive the light reflected from the outer non-substance detected area where the substance is not present on the outer surface of the planner light-transmissive member and transmitted through the transparent face of the optical device;
- a second light receiving member to receive the light guided by the light-guiding member and reflected from the inner substance detected area where the substance is present on the inner surface of the planner light-transmissive member;
- and
- a foreign substance detection processor to detect the substance present on the outer surface of the light-transmissive plane member based on the receiving result of the first light receiving member, and detect the substance present on the inner surface of the planner light-transmissive member based on the receiving result of the second light receiving member.