Provided is a socket structure capable of preventing or inhibiting defective attachment/detachment thereof and defective movement and defective sealing of a valve mechanism due to a solid deposit caused by a fluid. A socket used by connecting the socket to a plug of a connector includes a socket body in which a channel is formed and which has a valve mechanism; and a sleeve which is disposed so as to be slidable in an axial direction thereof and rotatable along an outer circumferential surface of the socket body. The socket is configured to be screwed and secured by inserting and connecting an entrance of the channel that opens at a lower end of the socket body to a plug exit that opens at an upper end of the plug and then a sleeve thread portion is screwed into a socket female thread portion by rotating the sleeve.