A heating apparatus which is assembled by inserting a columnar heating wire heater 2 into a hole 30 provided in a case 3, and heats cooling water introduced into the case 3 by the heating wire heater 2, wherein the heating wire heater 2 is inserted into boss portions 42 and 43 provided in the case 3, both end portions are supported by O-rings 50 disposed between inner peripheral walls of the boss portions 42 and 43 and an outer peripheral wall of the heating wire heater 2, a gap 45 for passing the cooling water is formed along an outer peripheral surface of the heating wire heater 2 between the two boss portions 42 and 43 within the case 3, and a tapered portion 60 and a rounded portion 61 are formed on an end portion on an insertion-direction distal end side of the heating wire heater 2.