Abstract: A theftproof device for a computer according to the present invention is provided. The theftproof device includes a PCB installed in a predetermined portion of the inside of a computer, an external connector portion provided on one side of the PCB for connecting to external cables, a vibration sensor installed on the PCB for sensing vibrations of the main frame of the computer, an alarm installed on the PCB for sounding an alarm when the main frame of the computer vibrates, a circuit provided on the PCB for receiving a signal input through the external connector portion and a signal from the vibration sensor, controlling the alarm, and performing communications with the computer system, and dip switches for setting the communication state between the circuit and the computer system.