An apparatus for auto-regulating the input power source of a driver is provided. The apparatus includes a load detector and a controller. The load detector detects a load current and outputs a detection signal according to the load current. The controller is coupled to the load detector and receives the detection signal. The controller provides an operation voltage between a first voltage and a second voltage, wherein the first voltage is lower than the second voltage. The operation voltage is supplied to the driver and regulated flexibly according to different load demand. In the light loading, the device for auto-regulating the input power source can improve the use efficiency of electric power.