An endoscope objective optical system includes an optical-path deflecting prism group and a lens group. A visual-field direction of the endoscope objective optical system is variable by moving a prism in the optical-path deflecting prism group. The optical-path deflecting prism group includes, in order from an object side, a first prism, a second prism, and a third prism, which are disposed to be in mutual proximity. The visual-field direction is variable to a first direction by the first prism undergoing a rotational movement with respect to the second prism, and the visual-field direction is variable to a second direction which differs from the first direction, by the first prism and the second prism undergoing rotational movement integrally with respect to the third prism.
