To provide a power source device reducing noise leakage to an AC power source.

A switch circuit 100 and a lamp HL1 are serially connected to the input terminals 1 and 2 of the AC power source through noise filters L1 and C1. To the switch circuit 100, electric field effective transistors Q111 and Q121 are serially connected in the form of directly connecting their source terminals with each other to supply a pulse width modulating signal of a frequency sufficiently higher than the frequency of the AC power source between a source and a gate. Thus, the circuit 100 is turned on/off by a frequency sufficiently higher than the frequency of an inputted AC power source and noise generated at the time is sufficiently blocked by a noise filter and is never leaked to the side of the AC power source.