The in-vehicle communication device includes a CAN communication unit, an Ethernet communication unit, a controller that controls communication by the CAN communication unit and the Ethernet communication unit, a first voltage output unit that outputs a first voltage, and a second voltage output unit that outputs a second voltage lower than the first voltage. The second voltage output is applied to the Ethernet communication unit. The first voltage output by the first voltage output unit and the second voltage output by the second voltage output unit are applied to the CAN communication unit. An opening/closing unit is provided between the second voltage output unit and the Ethernet communication unit. When a predetermined operation in the vehicle has been detected, the controller puts the opening/closing unit into an open state and cuts off the supply of power from the second voltage output unit to the Ethernet communication unit.