An orbital vibration generator means comprising, in addition to a clamp 4, 5 for holding a pair of thermo plastic pipes coaxially and a pressurizing means 2, 3, 14 for bringing into contact under a pressure junction end faces of a pair of thermo plastic pipes 10, 11 held by these clamps, a crank shaft 8 having a shaft portion 8a and a crank portion 8b in which the axes of these shaft portion 8a and crank portion 8b are eccentric, a motor 6 for giving rotation to the crank shaft 8, a bearing 9 attached to the crank portion 8b of said crank shaft 8, and a orbital vibration clamp 13 holding pipe an end portion of a thermo plastic pipe, formed integrally with the outer ring of the bearing 9 to move integrally with said bearing.