To provide a heater obtaining a faucet having a uniform thickness when end of a synthetic resin tube is radially enlarged by heaving to soften the end to a uniform temperature.

An external heater 2 is disposed on an outer periphery of a cylinder 1, and a heating chamber (a) is formed at an inner peripheral side of the cylinder 1. An opening 11 to which an end of a synthetic resin tube P is inserted is formed at one end side of the cylinder 1, blocked at the other end side by a shielding plate 12, and a vent hole 121 communicating with the exterior of the chamber (a) is formed at an upper part of the plate 12. An internal heater 3 protruding from a center of the plate 12 to the opening 11 side is provided in the chamber (a). An air diffusing tube 4 is provided substantially concentrically with the heater 3. Thus, the end of the tube can be heated at a uniform temperature in a circumferential direction.