Provided is a socket which hermetically seals a contact space in which plug-side contacts and socket-side contacts are in contact with each other by a small-scale simple structure. The socket includes an elastic seal member that surrounds one or a plurality of socket-side contacts, is fixed to an inner surface of an accommodation recess, and makes elastic contact with an exposure surface of a plug connection portion accommodated in the accommodation recess, a plug-side contact or contacts being exposed in the exposure surface. A contact space in which the plug-side contact(s) of the plug connection portion slid to a connection position in the accommodation recess and a contact portion or portions of the corresponding contact-side contact(s) make elastic contact with each other is surrounded and hermetically sealed by the inner surface of the accommodation recess, the elastic seal member, and the exposure surface of the plug connection portion.