A socket includes a main body section, a terminal provided in the main body section and assuming a cylindrical shape, a lead wire being welded to an end face provided at one end portion of the terminal, and an insulating section provided on the inside of the terminal, including a hole section through which the lead wire is inserted, and containing resin. When the cross sectional dimension of the lead wire is represented as W and the opening dimension of the hole section on the end face side is represented as “a”, the socket satisfies the following expression: 1.5 W≦a≦2.5 W.