The invention verifies the validity of instructions transmitted between controllers without complicating the structure of the electrical connection between controllers. The initial setup detection unit detects whether an initial setup of the lower communications network has been completed. When a fault in the path to the storage unit has been detected by the fault detection unit, the switching request output unit outputs a switching request signal to the switching permission unit. When the preparation status detection unit is aware that the lower communications network has completed initial setup, the preparation status detection unit outputs the preparation complete signal to the switching permission unit. When both the switching request signal and the preparation complete signal are input, the switching permission unit outputs the switching signal to the path switching unit. The path switching unit switches the path in accordance with the signal from the switching permission unit.
