An endoscope system includes an objective optical system, an optical-path splitter which acquires two optical images with different focus, an image sensor which acquires the optical images. The objective optical system includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. Switching to a normal observation and a close observation is possible by moving the second lens group toward an image side. The first lens group includes a first lens having a negative refractive power, and at least one positive lens, and the following conditional expressions (1)′；″；, (2), and (3)′；″； are satisfied:1.40≥；D_2T/fw<；5 ； ；(1)′；″；1.01<；ω(wide)/ω(tele)<；3.0 ； ；(2)2.70≤；D_1G/D_2T<；3.21 ； ；(3)′；″；.
