A signal transmission device is installed on a motherboard and is electrically connected to a signal control unit and a display output interface. The signal transmission device includes a signal receiving port, a signal output port, and a printed circuit connecting port. The signal receiving port is used for receiving a signal transmitted from the signal control unit. The signal output port is used for single output of the signal to the display output interface. The printed circuit connecting port is used for transmitting the signal from the signal receiving port to the signal output port. Thus, the signal transmission device may be used for single signal output so as to replace a switch integrated circuit of selective signal output. In such a manner, related circuit redesign and manufacturing cost may be reduced accordingly when the motherboard signal output design is changed from selective signal output to single signal output.