The present invention is an electronic device having a first device and a second device for reducing power consumption of a computer motherboard. When the computer motherboard is at an S4 or S5 state of an ACPI, the electronic device makes the computer motherboard enter like G3 mechanical off state of the ACPI. The second device determines that when the S4 or S5 state happens makes the first device to cut off a portion of electric components, for example the SIO chip and Southbridge chip, consuming stand-by power, and only supply the stand-by power to the electronic device itself. After the user pressed the power button, the second device will control the first device to connect the stand-by power to the computer motherboard.