An adaptor including: first and second optical systems a prism comprising a mirror region, first light flux and second light flux from the respective optical systems, being incident on the prism, the light flux passing through the prism at a portion, the second light flux being reflected by a mirror region after passing through the portion, the light flux emitted from the prism to a region and a light-shield at the region, the light-shield shields one of the first and second light flux and is disposed proximally to the prism relative to an imaging system of the endoscope when the adaptor is attached to an endoscope the first optical system is disposed such that the first light flux is incident in a direction parallel to an optical axis, the second optical system is disposed so that the second light flux is incident in a direction orthogonal to the optical axis.
