To efficiently save power consumption in a DC-DC converter part and also to effectively suppress the level of generated high-frequency noise by including an active LPF part and the DC-DC converter part for applying a D.C. power source voltage.

A low-pass filter circuit is provided with the DC-DC converter part 15 which receives the apply of the D.C. power source voltage from a power source part 14 and generates the higher D.C. power source voltage and a power source control circuit part 16 which is connected to the output terminal of the DC-DC converter part 15, supplies current based on the D.C. voltage which is applied from the DC-DC converter part 15 and permits load current to be small, which is permitted to flow from the DC-DC converter part 15 under a state, where the D.C. output voltage is almost fixedly kept in the active LPF part 13 in comparison with load current which is permitted to flow from the DC-DC converter part 15 under the state where a capacitance element 21 is charged, in order to ascend the D.C. output voltage in the active LPF part 13.