The disclosed is the power saving device capable of reducing power consumption by maintaining a constant output voltage even when an input voltage changes, and more particularly, the power saving device capable of improving the performance and lifespan of a load by stably adjusting a supplied voltage through the toroidal core, the multi-channel switch, and the control means for controlling the same and then supplying it to the load side and also reducing power consumption accordingly, and particularly, safely and firmly fixing the toroidal core in which the primary coil and the secondary coil are wound inside the power saving device by using the core fixing members and also preventing a temperature rise by easily discharging the heat generated in the toroidal core out of the device.