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 & lt; fF / f & lt; 1.3 (1) 1.7 & lt; fR / f & lt;2.7 (2) 0.63 & lt; | fF / fR | & lt; 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.