A vehicle system configured to control a vehicle provided with a vehicle platform that includes a drive unit, an auxiliary device, a first controller, a second controller, a high-voltage electric power source, a low-voltage electric power source, an autonomous driving platform that performs autonomous driving control, and a vehicle control interface that connects the vehicle platform and the autonomous driving platform to each other and is configured to convert a first control instruction into a second control instruction with respect to the vehicle platform, and transmit the second control instruction. The vehicle system includes a controlling device configured to cause the second controller and the vehicle control interface to enter an operating state and cut off supply of electric power from the high-voltage electric power source to the drive unit.