Power is supplied and a communication path secured by connecting various accessories to branch lines, each of which branches from a main line included in backbone structures. Control of power distribution and the like is implemented by communication between higher-level control units arranged in a smart power supply box, for example, and lower-level control units arranged in area drivers, for example. A switching circuit is arranged at a connection location between the main lines and the branch lines, and is automatically switched such that the terminals to be connected are coordinated. Specifications such as the current of multiple terminals on the power supply side are commonly fixed, and the power to be distributed is controlled by switching the number of terminals to be used. Component standardization and a reduction in part numbers are made easier. The connection position can be freely changed.