PURPOSE: To increase the efficiency in piping work by making a position of a three-way pipe joint (T joint) adjustable in the vertical direction, and absorbing an installing error of branch pipes when the branch pipes of the respective floors are connected to a main drain pipe in a pipe space.

CONSTITUTION: At least one of upper and lower connecting parts 20a and 20b on the main drain pipe 6 side of a three-way pipe joint 18 is formed as a plug-fit type 19 whose inserting length (superposing margin) is made large. Next, drain branch pipes 65 arranged on every floor of the respective floors are connected to the main drain pipe 6 through a pipe joint 18. In this case, when the pipe joint 18 and the main drain pipe 6 are connected to each other, on a dimensional error of a building frame or a vertical directional error caused by an installing error of the branch pipes 65, an inserting quantity of the main pipe 6 is adjusted, and they are fixed together. Even if disorder is caused more or less in the vertical direction in the branch pipes 6, they are made connectable to the main pipe 6 without amending the building frame or the inside of a house. Thereby, piping work can be efficiently performed.