To provide a resistance heater which enables detection of short- circuiting between a heating container and an energizing circuit for the resistance heater by a simple circuit.

In order to heat a heating space inside a conductive container 3, a plurality of resistance heaters set in the container 3 are connected to the secondary side of a three-phase AC transformer 2. To the secondary side of the three-phase transformer 2, detection elements 5 to be star-connected. A means for detecting the voltage between the container 3, and a neutral point O in the star-connection is provided.