Each processor comprises a register for storing start address of a forked child thread and a comparator for detecting that the value of its own program counter is coincident with the start address stored in this register. The system includes at least one wireless device having a first RF transceiver and a first microprocessor operably coupled to the first RF transceiver. The driving control device does not generate either the driving force or the braking force, and allows the vehicle to drive inertially, when the operation quantity ranges from the first threshold value to the second threshold value.