An endoscope system consists mainly of: an endoscope having a solid-state imaging device and an objective optical system that converges an object image on said solid-state imaging device; and a signal processing unit that processes an image signal produced by the endoscope so as to produce a video signal. The objective optical system includes an optical phase modulation member. The optical phase modulation member exhibits a response of 0.2 or more derived from an optical transfer function relative to a spatial frequency on the solid-state imaging device determined based on the Nyquist theorem, that is, a Nyquist frequency, over a wider range of distances than a depth of field offered by an objective optical system not having the optical phase modulation member.