To provide a flush stool, which can be used for floor drain and for wall drain in common and installation works of which are also simplified.

A piping box 3, in which an underside is opened and connecting openings 2 are formed to a side face plate 1, is joined and mounted on the rear side of a stool body 4. A drain inlet 5 formed at the rear section of the stool body 4 and either one selected from the connecting openings 2 of the piping box 3 or a drain pipe port 7 shaped to a toilet floor face 6 are connected and joined through a drain pipe 8 housed and piped in the piping box 3.