There is provided an endoscope objective optical system which enables to change a field of view to an arbitrary direction without bending an endoscope, even in a narrow space.In the endoscope objective optical system which includes an optical-path deflecting prism group PG and a lens group LNS, and in which, a visual-field direction A is let to be variable by moving a prism in the optical-path deflecting prism group, the optical-path deflecting prism group PG includes in order from an object side, three prisms namely, a first prism P1, a second prism P2, and a third prism P3, and the first prism P1, the second prism P2, and the third prism P3 are disposed to be in mutual proximity, and the visual-field direction A is let to be variable to a first direction DR1 by the first prism P1 undergoing a rotational movement with respect to the second prism P2, and furthermore, the visual-field direction A is let to be variable to a second direction DR2 which differs from the first direction DR1, by the first prism P1 and the second prism P2 undergoing rotational movement integrally with respect to the third prism P3.
