In connecting a flushing port (2) of a toilet stool (1) which is formed so as to face the floor surface to which the toilet stool (1) is installed to a drainpipe (3) of the building, the connection is made by means of a flushing-side connecting pipe (6) which connects to the flushing port (2), a drain-side connecting pipe (7) which connects to the drainpipe (3), and a linking pipe (8) which makes connection between the above-noted two pipes. In making the pipe connections, the linking pipe (8) is cut off in accordance with the distance between the flushing port (2) and the drainpipe (3) or pipe insertion overlap can be used to adjust the length of the linking pipe (8).