A checking ECU 45 controls, in step S11, an electromagnetic clutch 31 into a disconnected state in a state where a turning electric motor 22 is stopped, and acquires a steering angle \u03b8 and a steering torque T in step S12. The cross-sectional area of the common gas flow channel portions is smaller than the sum of the cross-sectional areas of non-common gas flow channel portions that are located upstream of a confluent portion. In response to detecting the memory location being accessed, it is determined whether a monitor bit corresponding to a hardware thread in the memory location is set.