To provide a waterproof heating mat for a bathroom or the like that is safe in terms of electricity and structure.

In the manufacturing method, a heater unit 2 having a support 2c for fixing a heater wire 2a and a temperature detector 2b on a rear material 3, the surface of the heater unit 2 that is coated with an adhesive in advance and the rear material 3 affixed to the surface of a surface material 1 that is coated with an adhesive in advance, and the heater unit 2 is pinched between the rear and surface materials 3 and 1 and rear and surface materials 3 and 1 are integrated by an adhesive. By the manufacturing method, the entry of moisture into the heater unit 2 is prevented for improving electric waterproofness. Also, the amount of required adhesives is equally dispersed to each surface for uniform coating to each entire surface, and the entire surface of the rear and surface materials 3 and 1 can be bonded surely for also improving productivity.