To reduce the loss of a power supply device with a step-up type active filter in a low output state and practice protective operation, in which the abnormality of an active filter circuit is detected and the input is cut off.

The average value of a current which is applied to the switching device Q2 of a converter circuit CONV is obtained by an average circuit detection circuit HB8 and is compared with a reference voltage Vref1 by a comparator CP1. The operation of an active filter control circuit HB1 is stopped based on the comparison result to avoid decline in the I/O efficiency of a power supply device in a reduced output power state, such as a low current consumption mode. Further, the average value of a current applied to a switching device Q1 of an active filter AF is obtained by an average current detection circuit HB10 and is compared with the average value obtained by the average current detection circuit HB8 by a comparator CP2. If the difference between the two average values is not less than a predetermined value, an AC input is cut off via a relay RL1.