A leaning-vehicle-steering-actuator controller for a leaning vehicle , the leaning vehicle including: a vehicle body frame configured to lean in a leaning-vehicle-leftward direction when the leaning vehicle is turning left and to lean in a leaning-vehicle-rightward direction when the leaning vehicle is turning right; at least one steerable wheel supported by the vehicle body frame ; a handlebar configured to be manipulated by a rider to steer the at least one steerable wheel , and supported by the vehicle body frame in a rotatable manner; a steering actuator configured to apply a torque to the at least one steerable wheel to steer the at least one steerable wheel ; and a roll rate sensor configured to detect a roll rate that is an amount of change per unit time of a roll angle of the vehicle body frame around a roll axis (Ax) extending along a leaning-vehicle-front-back direction, the roll angle changing as the vehicle body frame is rotating around the roll axis (Ax); wherein the leaning-vehicle-steering-actuator controller is configured to control the steering actuator by using the roll rate sensor without using a torque sensor configured to detect a torque generated around a rotation axis of the handlebar by a rider's manipulation and based on the roll rate obtained from the roll rate sensor , and not the torque detected by the torque sensor as the torque generated around the rotation axis of the handlebar by the rider's manipulation, characterised in that the leaning-vehicle-steering-actuator controller is configured to control the steering actuator by using the roll rate sensor using neither the torque sensor configured to detect the torque generated around the rotation axis of the handlebar by the rider's manipulation, nor a roll sensor configured to detect the roll angle, and based on the roll rate obtained from the roll rate sensor , neither the torque detected by the torque sensor nor the roll angle detected by the roll sensor. a vehicle body frame configured to lean in a leaning-vehicle-leftward direction when the leaning vehicle is turning left and to lean in a leaning-vehicle-rightward direction when the leaning vehicle is turning right; at least one steerable wheel supported by the vehicle body frame ; a handlebar configured to be manipulated by a rider to steer the at least one steerable wheel , and supported by the vehicle body frame in a rotatable manner; a steering actuator configured to apply a torque to the at least one steerable wheel to steer the at least one steerable wheel ; and a roll rate sensor configured to detect a roll rate that is an amount of change per unit time of a roll angle of the vehicle body frame around a roll axis (Ax) extending along a leaning-vehicle-front-back direction, the roll angle changing as the vehicle body frame is rotating around the roll axis (Ax); wherein the leaning-vehicle-steering-actuator controller is configured to control the steering actuator by using the roll rate sensor without using a torque sensor configured to detect a torque generated around a rotation axis of the handlebar by a rider's manipulation and based on the roll rate obtained from the roll rate sensor , and not the torque detected by the torque sensor as the torque generated around the rotation axis of the handlebar by the rider's manipulation, characterised in that the leaning-vehicle-steering-actuator controller is configured to control the steering actuator by using the roll rate sensor using neither the torque sensor configured to detect the torque generated around the rotation axis of the handlebar by the rider's manipulation, nor a roll sensor configured to detect the roll angle, and based on the roll rate obtained from the roll rate sensor , neither the torque detected by the torque sensor nor the roll angle detected by the roll sensor. <EOS>