A connection assembly includes an optical electronic part and a socket. A conductive pad connected to a photoelectric conversion element of the optical electronic part is oriented with imaging field of view upward, and slidably contacts a contact of the socket. The optical electronic part includes an insulating case with a flange protruding along a horizontal plane, and a conductive pad that is exposed in an outer surface parallel to the horizontal plane. The socket includes a guide portion that slidably guides the flange portion along the horizontal plane, and a contact fixed to a housing opposed to the outer surface in which the conductive pad is exposed, with a contact portion located in a movement locus of the conductive pad sliding with the flange portion along the horizontal plane. As the insulating case is operated, the contact makes sliding contact with the conductive pad to provide a self-cleaning effect.