PURPOSE: To strongly connect a metal pipe and a synthetic resin pipe.

CONSTITUTION: The cylindrical body of a metal sleeve 3 is inserted in the end part of a synthetic resin pipe 2 to bring the flange of the sleeve 3 into contact with the end surface of the pipe 2 and, thereafter, the end part of the synthetic resin pipe 2 is inserted in a receiving port 11 to engage the flange of the sleeve 3 with the stopper step part 14 provided to the deep part of the receiving port 11. Subsequently, a diameter expanding jig 5 is inserted in the synthetic resin pipe 2 to expand the diameter of the sleeve 3 to allow the outer peripheral surface of the end part of the synthetic resin pipe 2 to bite into the unevenness 12 provided to the inner peripheral surface of the receiving port 11. By this method, the metal sleeve can be expanded in its diameter without positionally shift the metal sleeve and, therefore, the metal sleeve and the synthetic resin pipe are strongly bonded.