A software update device comprising: an inlet to which an outlet of a slow charging cable is connected; a Control Pilot, CP, monitoring unit configured to monitor a CP voltage applied through a CP line from the controller of the slow charging cable when the slow charging cable is connected to the inlet; a mode switching request unit configured to request mode switching to the controller of the slow charging cable by converting the monitored CP voltage to a preset mode switching voltage; a communication switching unit configured to connect a Local Interconnect Network, LIN, transceiver for LIN communication to the CP line when the controller of the slow charging cable is switched to a LIN communication mode for software update; and a control unit configured to control the LIN transceiver to transmit a pre-stored software update file to the controller of the slow charging cable; wherein the mode switching request unit is a switch of which an input terminal is connected to the CP line and of which an output terminal is connected to a resistor and ground; wherein the mode switching request unit is turned on/off under the control of the control unit, and is provided to lower the CP voltage of the CP line to the preset mode switching voltage by resistor when turned on; and wherein the controller of the slow charging cable comprises: a CP driver configured to apply a CP voltage through the CP line; a LIN transceiver for LIN communication; and a switch disposed on the CP line and selectively connected to any one of the input terminal of the CP driver and the input terminal of the LIN transceiver, wherein when a mode switching request for updating software is recognized through the preset mode switching voltage, the controller of the slow charging cable connects the switch connected to the input terminal of the CP driver to the LIN transceiver so as to switch to a LIN communication mode for software update. an inlet to which an outlet of a slow charging cable is connected; a Control Pilot, CP, monitoring unit configured to monitor a CP voltage applied through a CP line from the controller of the slow charging cable when the slow charging cable is connected to the inlet; a mode switching request unit configured to request mode switching to the controller of the slow charging cable by converting the monitored CP voltage to a preset mode switching voltage; a communication switching unit configured to connect a Local Interconnect Network, LIN, transceiver for LIN communication to the CP line when the controller of the slow charging cable is switched to a LIN communication mode for software update; and a control unit configured to control the LIN transceiver to transmit a pre-stored software update file to the controller of the slow charging cable; wherein the mode switching request unit is a switch of which an input terminal is connected to the CP line and of which an output terminal is connected to a resistor and ground; wherein the mode switching request unit is turned on/off under the control of the control unit, and is provided to lower the CP voltage of the CP line to the preset mode switching voltage by resistor when turned on; and wherein the controller of the slow charging cable comprises: a CP driver configured to apply a CP voltage through the CP line; a LIN transceiver for LIN communication; and a switch disposed on the CP line and selectively connected to any one of the input terminal of the CP driver and the input terminal of the LIN transceiver, a CP driver configured to apply a CP voltage through the CP line; a LIN transceiver for LIN communication; and a switch disposed on the CP line and selectively connected to any one of the input terminal of the CP driver and the input terminal of the LIN transceiver, wherein when a mode switching request for updating software is recognized through the preset mode switching voltage, the controller of the slow charging cable connects the switch connected to the input terminal of the CP driver to the LIN transceiver so as to switch to a LIN communication mode for software update.