A current detecting device and method that detects a variation in a current being supplied to a load in supplying variable DC power to the load via an inductor from a synchronous rectification DC-DC converter in which a high-side switch is connected to one electrode of a DC input voltage source and a low-side switch connected to the other electrode. The switches are turned on and off alternately during a prescribed switching period. A low-pass filter is connected to a signal line that leads from a connecting point of the inductor and the switches. An operation circuit detects an output current of the DC-DC converter by performing an operation on the difference between an output voltage of the low-pass filter and an output voltage of the DC-DC converter.