To provide the control circuit of the phase controller of simple constitution which has small variation in load electric power even if the source voltage varies.

The control circuit 2, controlling the phase controller 1 which controls the electric power supplied to the load by performing phase control over the single-phase AC power source E by using switch elements Ql and Q2, is provided with a source voltage detecting circuit 11, a reference voltage circuit 21, and a comparator CP which compares the output voltages of the source voltage detecting circuit 11 and reference voltage circuit 21 and outputs the result, and the output of the comparator CP is connected to the gate circuit of the phase controller 1.