An actuator includes a motor, a rotation transmitting member, a reverse input preventing device, a converting device, and a rod. The motor includes a rotating shaft. The rotation transmitting member is configured to transmit rotation of the rotating shaft. The reverse input preventing device includes an input member and an output member. The reverse input preventing device is configured to prevent external force input to the output member from being transmitted to the input member. The converting device includes a nut that rotates according to the rotation of the output member. The converting device is configured to convert a rotary motion of the nut into a linear motion. The rod is configured to advance and retract according to the linear motion of the converting device. The input member and the rotation transmitting member are integrated. The output member and the nut are integrated.

To achieve a fail-safe fully utilizing the advantage of plural motors, a second controller performs a one-motor SBW mode when at least one of a first turning controller, a first turning motor and a torque sensor malfunctions in a state where the first turning controller and the second turning controller perform a two-motor SBW mode. Furthermore, the first controller performs a one-motor EPS mode when at least one of the second turning controller and the second turning motor malfunctions in the state where the first turning controller and the second turning controller perform a two-motor SBW mode.

To suppress a voltage drop of a battery in an idle reduction state, a vehicle includes an idle reduction function of stopping the idling of the engine and restarting the engine when the vehicle starts moving. Then, a steering-by-wire control processing is performed to disengage a clutch and to control driving of turning motors. When the idling of the engine is stopped by the idle reduction function, a disengaged state of the clutch is maintained and the driving of the turning motors is restricted.

One example steering mechanism includes a first steering gear, where the first steering gear is configured to convert obtained driving force to transmit driving force to an outer-side wheel during steering, to control steering force applied to the outer-side wheel. The example steering mechanism includes a second steering gear, where the second steering gear is configured to convert obtained driving force to transmit driving force to an inner-side wheel during steering, to control steering force applied to the inner-side wheel. The first steering gear and the second steering gear are connected by using a first clutch. If the first clutch is in a disengaged state, driving force is not transmitted between the first steering gear and the second steering gear. If the first clutch is in an engaged state, driving force is transmitted between the first steering gear and the second steering gear.