A socket is configured to hold a straight tube type lamp including an earth pin including a leg portion, and a holding portion formed at a distal end of the leg portion, formed into an oval shape and having a diameter larger than that of the leg portion. The socket includes a socket body, a guiding device, and terminals. The socket body includes an insertion port having a dimension larger than a short diameter dimension of the oval shape of the holding portion of the earth pin and a notched portion communicating from the insertion port to a predetermined holding position P where the earth pin is held and allowing the leg portion of the earth pin to be inserted therethrough. The guiding device is configured to guide the holding portion to the predetermined holding position P by a rotation of the earth pin between the insertion port and the predetermined holding position P. The terminals hold the holding portion of the earth pin at the predetermined holding position P.