To provide a lens adaptor for visible light/infrared light photography, the adaptor suppressing image quality degradation when the visible image and the infrared light image of a subject are formed at different positions from each other through a single photographic lens.

The lens adaptor includes: a color separating optical system P that separates light from a subject 1 passed through the photographic lens 10, into visible light and infrared light; an incident side relay lens RL1 that is disposed in an optical path extending to the color separating optical system P, for relaying a first optical image formed by passing the light through only the photographic lens 10; a visible light relay lens RL2 that is disposed in the optical path of visible light, for relaying the first optical image through the incident-side relay lens RL1, thereby forming a visible light image Mk; and an infrared light relay lens RL3 that is disposed in the optical path of infrared light, for relaying the first optical image through the incident relay lens RL1, thereby forming an infrared optical image Ms. Thus, the visible light image Mk and the infrared light image Ms showing the subject 1 are formed at different positions from each other.