To make a connecting device applicable, with a simple structure, to an existing multifiber optical connector 10, and to make sure connection possible.

The connecting device includes: a first holder 400 which is attachably/detachably engaged with one end opening of a housing 500 and which, with a first multifiber optical connector 10a inserted, stores and holds this connector 10a; an energizing means which comes in contact with a second multifiber optical connector 10b to energize it to the first multifiber optical connector 10a and which is composed of a spring 140, a guide pin supporting member 300 and the like; and a second holder 200 which, detachably engaged with the other end opening of the housing 500, holds the energizing means.