An oblique-view objective optical system is constituted by a front lens group GF composed of a negative lens, an optical path conversion element P, a stop S, and a rear lens group GR with a positive refractive power in order from an object side. The rear lens group GR is composed of a positive lens L2 and a cemented lens with a positive refractive power. The cemented lens is constituted by a positive lens L3 and a negative lens L4 in order from the object side. The oblique-view objective optical system satisfies the following conditional expressions (1), (2), and (3):−2.0 < fF / f < −1.3 (1)1.7 < fR / f <2.7 (2)0.63 < fF / fR < 0.88 (3)Where fF represents the focal distance of the front lens group fR represents the focal distance of the rear lens group and f represents the focal distance of the whole oblique-view objective optical system.
