To surely prevent pulling-out of pipes by a simple means by providing a first locking part disengageably engaged with a collection pipe, a second locking part disengageably engaged with a horizontal branch pipe and a connecting part for disconnectedly connecting the first and second locking parts with each other.

For connecting the end part of a horizontal branch pipe 4 to a collection pipe 1 in a socket 5, first a pair of semi-circular bands 13 are disposed like a ring, the ring part of a round annular bolt 17 is inserted between the end parts thereof and the bolt 15 and the nut 16 of a connecting means 14 are engaged. Then, after the end part of the horizontal branch pipe 4 is inserted into a locking part 9, the horseshoe type metallic material 11 of a locking part 8 is locked in the outer peripheral surface of the socket 5. Then, the end part of the horizontal branch pipe 4 is slightly inserted into the socket 5, the round annular bolt 17 of a connecting part 10 is inserted into the bolt through-hole 12 of the horseshoe type metallic material 11 and the nut is engaged therewith. Then, the horizontal branch pipe 4 is inserted until the end part of the horizontal branch pipe 4 comes into contact with the bottom of the socket 5, the nut 16 is fastened and the semi-circular bands 13 are fixed to the horizontal branch pipe 4.