In a fluid-transfer coupling device (5) that connects a plug (70) and a socket (10) to each other to communicate respective flow paths in the socket and the plug with each other, the plug includes, at least, an inner spacer (74) having an inner passage (78) formed to allow a passage of fluid, a plug collar (73) covering the outer circumferential surface of the inner spacer and a flange (75) formed on a proximal end of the plug to connect the plug to a conduit. The plug collar and the flange are made of metal. Consequently, even if the flow rate of the fluid is large, the plug can be firmly supported in the device. The inner spacer is made of a resinous material. In this connection, at least one portion of an outer circumferential portion of the plug may be formed of metal.