An endoscope includes in order from an object side to an image side, an objective optical system, an optical-path splitter which splits light from the objective optical system into two, and an image sensor which picks up two split images.
A multi-order λ/4 wavelength plate made of a birefringent material is disposed in an optical path between the objective optical system and the optical-path splitter, and the multi-order λ/4 wavelength plate satisfies the following conditional expressions (1) and (2)′. 10≤(d/d0)×0.25≤85  (1) 0.08