PURPOSE: To stabilize the operation of all load circuits by providing reverse-current stopping diodes and capacitors corresponding to load circuits and by supplying across voltages of respective capacitors as electric power sources of load circuits.

CONSTITUTION: Reverse-current stopping diodes D5∼D8 and capacitors C1∼C4 are provided corresponding to load circuits LD1∼LD4 in a public telephone set and series circuits of D5∼D8 and C1∼C4 are connected in parallel to Zener diode ZD. By Zener voltage Vz of diode ZD, capacitors C1∼C4 are charged via diodes D5∼ D8 and across voltages of C1∼C4 are supplied to circuits LD1∼LD4 as their electric power voltages V1∼V4. Therefore, even if large load current flows to LD1, only the across voltage of capacitor C1 drops and across voltages of C2∼C4 stay unchanged, so that the operation of circuits LD2∼LD4 will be held stable. In addition, as each load finishes its operation, each capacitor is charged for the next operation.