An endoscope system includes an objective optical system OBL, an optical path splitting unit which splits an object image acquired by the objective optical system OBL into two optical images having a different focus, an image pickup element which acquires the optical images, and an image synthesis processing section which selects in a predetermined area an image with a relatively high contrast from the two optical images acquired, and generates a composite image, wherein the objective optical system OBL includes a first lens L1 having a negative refractive power which is nearest to object, and the endoscope system satisfies the following conditional expressions (1) and (2). 3