An voltage detection device includes a comparator circuit comprising a first input terminal connected to a system power supply, a second input terminal connected to a standby power supply, an output terminal capable of outputting a control voltage according to comparison result; an indicator circuit; and a switch circuit connected between the standby power supply and the indicator circuit, comprising a control terminal to receive the control voltage from the comparator circuit thereby to control the standby power supply supplied to the indicator circuit or not; a power state terminal of the computer connected to a node between the standby power supply and the indicator circuit, wherein the power state terminal is at a low level when the computer is turned off. The voltage detection device can ensure that all the power supplies provide power to the computer components normally.