current flows from the rectifier 1 to the output capacitor c1 through the rush current prevention resistor r1 choke coil l1 and the diode d1 thereby charging the output capacitor c1 consequently the voltage across the output capacitor c1 is raised towards the level of the peak voltage of the a c voltage supplied to the rectifier circuit 8 from the view points of efficiency and other factors the dc dc converter circuit 10 is preferably designed such that the minimum operation input voltage which can stabilize the output be set as high as possible the minimum operation input voltage is therefore set to a level which is between 0 9 to 1 0 times the peak value of the above mentioned a c voltage in such a case the dc dc converter circuit 10 starts to operate at a moment t2 at which the voltage v1 charged in the output capacitor c1 reaches the minimum operation input voltage so as to produce a stabilized output v3 when the dc dc converter circuit 10 has commenced the operation electrical current flows through the primary winding n1 of the converter transformer 4 so that voltages are induced in the secondary and ternary windings n2 and n3 consequently the power supply voltage v2 starts to rise so that a voltage is applied to the booster converter control circuit 2 the booster converter circuit 9 starts to operate at a moment t3 at which the power supply voltage v2 supplied to the booster converter control circuit 2 rises the voltage v1 charged in the output capacitor c1 connected to the output of the booster converter circuit 9 starts to rise as the booster converter circuit 9 starts to operate the voltage v1 across the output capacitor c1 after reaching the level.