To provide an energy-saving heater for heat-treating furnace that can prevent the occurrence of outward thermal diffusion even when the working temperature of a heat-treating furnace is high.

A first cylindrical body 3 is provided on the outer periphery side of a cylindrical heat insulating wall 2 covering a heating element 1, and a second cylindrical body 4 is provided on the outside of the outer periphery of the first cylindrical body 3. In addition, a vacuum insulating layer 12 is formed between the first and the second cylindrical bodies 3 and 4 so as to prevent outward heat transfer from the first cylindrical body 3 when the working temperature of the heat-treating furnace exceeds a prescribed value.