A heating device which can prevent unused active chemical species from attaching to the bodies of various vacuum devices or depositing on the inner wall of their exhaust pipes to thereby be able to make the size of exhaust pipes smaller than before and make the exhaust pipe maintenance easier. The heating device comprises a heat resisting vacuum insulator (4) wound around the outer periphery of an electric heater (3) disposed along the outer wall of an exhaust pipe (1), wherein the electric heater (3) has a resistance heating element and a heat resisting electric insulator covering this resistance heating element, and the heat resisting vacuum insulator (4) comprises a hollow platy covering material air-tightly sealed thereinside by a metal seat (5) having a heat resisting temperature of at least 100° C., and a fibrous or granular filling material (6) filled in the hollow portion of this covering material and having a heat resisting temperature of at least 100° C., the inside of the covering material being kept vacuum.