PURPOSE: To detect an abnormal condition at a low cost by providing a winding round a noise-controlling inductor core connected in series to a phase-controlling element and by detecting a pulse voltage generated between said windings so as to cause the detection circuit to operate.

CONSTITUTION: A phase controller supplies a load 2 with electricity from an AC power 1 via a phase-controlling element 3 such as TRIAC and a noise- controlling inductor 4. Further, there is provided a detection circuit 6 for detecting the abnormal condition of a current flowing through a power application path serially connecting said load 2 and inductor 4, which circuit is composed of a full-wave rectifying element 7, a capacitor 8 a resistance 9, a reference voltage source 10, a comparator 11 and an output terminal 12. In this case, a winding 13 insulated and wound once to several times is provided round the core of said inductor 4 apart from the winding of the inductor. Thus, a given voltage is normally generated between said windings 13 to enable detecting said voltage and then the failure and so on of the phase-controlling element 3 and the like.