To provide a power saving apparatus which can automatically change the reference voltage thereof corresponding to increase and decrease of voltage drop of a power line extended up to a load to realize extensive power saving effect without various procedures.

The power saving apparatus sets a rather higher reference voltage VH during the working hours of a factory up to 17:00 from 8:00 because a voltage drop of the power line to the load is large and sets the lower reference voltage VL during the non-working hours up to 8:00 from 0:00 and to 24:00 from 17:00 because the voltage drop is small. The power saving apparatus changes automatically the reference voltage depending on such settings. A voltage detecting means compares the detected voltage with the reference voltage to determine the degree of power saving, and then outputs an output voltage to a load depending on the reference voltage.