An object is to provide a coupling that prevents connection failure of a scope and a light source device and that is compatible with existing scopes as well as to provide an endoscope system having the same. A coupling employed includes a columnar plug and a socket into which the plug is inserted and connected. The plug has engaging projections that are radially projected from and retracted into an outer circumferential surface thereof. The socket has a connection surface to which an end surface of the plug is abutted, a pressing member having a through-hole that is slightly larger than the outside diameter of the plug, a coil spring that urges the pressing member along an insertion direction of the plug toward the connection surface, and stopper members that stop the pressing member so as to push it in a direction opposite to a direction toward the connection surface until the engaging projections pass through the through-hole in the pressing member. The stopper members stop pushing the pressing member after the engaging projections pass through the through-hole in the pressing member.