To provide a drain socket, which suppresses the weakening of a siphon action by joining drain from a flush toilet to that from another unit.

The drain socket (1) is used for the flush toilet (B) to join a drainage channel (B1) of the flush toilet (B) to a drainage channel (L1) for other drain (L) and connect the joined drainage to a drain pipe (D) laid under a floor surface (F). The drain socket (1) comprises a vertical pipeline (2), which has a socket inflow port (2a), which is connected to the drainage channel of the flush toilet (B), on the upper end of the pipeline (2) and extends almost vertically, a lateral pipeline (4), which connects the vertical pipeline (2) to the drain pipe (D) and extends laterally, and a buffering chamber (6), which is formed on the periphery of the vertical pipeline (2), and has a buffering chamber inflow port (6a) connected to the drainage channel for other drain (L) and a joined exit (6b) opening at the upper part of the lateral pipeline (4), which is near the drain pipe (D).