Abstract: An electric corrosion preventing apparatus with a circuit having an indication lamp for indicating an operation state of the apparatus, which is used for preventing an inside wall of a hot-water receptacle, such as a water heater and a boiler, from being corroded by rust. In the circuit, the secondary winding of a voltage-dropping transformer is provided with a couple of diode-capacitor combinations. Those diode-capacitor combinations, respectively, are used for rectifying positive and negative parts of a low AC voltage produced by the secondary winding into positive and negative DC voltages. A positive DC voltage is coupled with an electric corrosion prevention load while a negative DC voltage is coupled with a lamp load. With this circuit arrangement, the positive part of the AC voltage is used for the electric corrosion prevention while the negative part, for the lamp.