To provide a socket that can be made compact by absorbing variation in the length of a straight tube lamp, and can facilitate insertion of a lamp while preventing the lamp from falling easily.

The socket comprises a socket body 38 having a front face 31a, a rear face 35a and a side face 31 (31b, 31c), and provided with one ground pin insertion hole 32, in the front face 31a, for passing the tip of one pole ground pin projecting from the ground side cap of a straight tube LED lamp to be attached, a fixing leg 33 projecting from the side face 31 to the rear face 35a side and being inserted into the fixing hole of the fixing surface in order to guide the movement of the socket body 38 in the longitudinal direction, a claw 34 provided at the tip of the fixing leg 33 and hooked to the rim of the fixing hole so that the fixing leg 33 does not fall out from the fixing hole, and a spring 40 disposed on the rear face 35a.