PURPOSE: To inexpensively obtain the rush current suppressing circuit of a power source in which the rush current can be effectively suppressed with less components and which has high reliability.

CONSTITUTION: In a power source having a capacitor-input rectifying and smoothing circuit, a rush current suppressing circuit having a power fixed resistor 13 and a thermal resistance element 18 in which the resistance value is varied according to the surface temperature is inserted at least one of AC input line and a DC line after rectifying. At the time of starting, the resistance value of the resistor 13 and the normal temperature resistance value of the element 18 suppress the rush current. At the time of steady operation, the element 18 is heated after conducting to reduce its internal resistance, and hence only power loss by the resistor 13 of relatively small resistance value exists. Further, the rush current at the time of restarting after the power source is once stopped can be suppressed by the resistor 13.