To provide an endoscope having a variable diaphragm which has a smaller number of parts, and allows for a close-up observation by a simple mechanism which does not enlarge the diameter of the distal end part of an insertion unit.

For this endoscope, an objective optical system and an imaging surface on which an image is built up by the objective optical system are provided at the distal end part of the insertion portion. In the endoscope, in front of or behind the objective optical system, the variable diaphragm device which makes the diameter of a restriction concentric with the optical axis of the objective optical system variable is arranged.