A vehicle control device, comprising: a smoothing capacitor; a first drive circuit; a second drive circuit; a control circuit, wherein the vehicle control device is connectable to an on-board device mounted on a vehicle and is configured to control the on-board device mounted on a vehicle, wherein the on-board device includes a rotating electrical machine, and an engaging/disengaging mechanism having a function to permit and cut off torque transmission between a driven body that is rotationally driven by the rotating electrical machine and the rotating electrical machine, wherein the smoothing capacitor smoothens electric power that is applied from a power supply connectable to the vehicle control device and mounted on the vehicle, wherein the first drive circuit drives the rotating electrical machine with the electric power smoothed by the smoothing capacitor, wherein the second drive circuit drives the engaging/disengaging mechanism with the electric power smoothed by the smoothing capacitor, wherein the control circuit controls the first drive circuit and the second drive circuit, characterized by a switch which has a function to connect and disconnect the first drive circuit and the second drive circuit to and from the power supply, and is provided closer to the power supply such that the smoothing capacitor is interposed between the switch and the first and second drive circuits, wherein if an abnormal condition of the vehicle having the on-board device mounted thereon is detected in a state where the drive circuits are connected to the power supply, the control circuit switches the switch to disconnect the drive circuits from the power supply and supplies electric power generated by charge stored in the smoothing capacitor to the engaging/disengaging mechanism via the second drive circuit, wherein the abnormal condition is detected by using a change in impact on the vehicle as an index, and the control circuit controls driving of the engaging/disengaging mechanism so as to cut off the torque transmission, in the case where the control circuit supplies the electric power generated by the charge stored in the smoothing capacitor to the engaging/disengaging mechanism in response to the detection of the abnormal condition. a smoothing capacitor; a first drive circuit; a second drive circuit; a control circuit, wherein the vehicle control device is connectable to an on-board device mounted on a vehicle and is configured to control the on-board device mounted on a vehicle, wherein the on-board device includes a rotating electrical machine, and an engaging/disengaging mechanism having a function to permit and cut off torque transmission between a driven body that is rotationally driven by the rotating electrical machine and the rotating electrical machine, wherein a rotating electrical machine, and an engaging/disengaging mechanism having a function to permit and cut off torque transmission between a driven body that is rotationally driven by the rotating electrical machine and the rotating electrical machine, wherein the smoothing capacitor smoothens electric power that is applied from a power supply connectable to the vehicle control device and mounted on the vehicle, wherein the first drive circuit drives the rotating electrical machine with the electric power smoothed by the smoothing capacitor, wherein the second drive circuit drives the engaging/disengaging mechanism with the electric power smoothed by the smoothing capacitor, wherein the control circuit controls the first drive circuit and the second drive circuit, characterized by a switch which has a function to connect and disconnect the first drive circuit and the second drive circuit to and from the power supply, and is provided closer to the power supply such that the smoothing capacitor is interposed between the switch and the first and second drive circuits, wherein if an abnormal condition of the vehicle having the on-board device mounted thereon is detected in a state where the drive circuits are connected to the power supply, the control circuit switches the switch to disconnect the drive circuits from the power supply and supplies electric power generated by charge stored in the smoothing capacitor to the engaging/disengaging mechanism via the second drive circuit, wherein the abnormal condition is detected by using a change in impact on the vehicle as an index, and the control circuit controls driving of the engaging/disengaging mechanism so as to cut off the torque transmission, in the case where the control circuit supplies the electric power generated by the charge stored in the smoothing capacitor to the engaging/disengaging mechanism in response to the detection of the abnormal condition.