In a steering control device, method, and system, a command is calculated for generating a periodical yaw moment having a phase opposite to oscillating motion based on information on oscillating motion which occurs in a vehicle combination composed of a vehicle and a trailer, and based on the calculated command, a first steering angle command for controlling a steering angle of the front wheels of the vehicle is output to a front wheel steering control unit and a second steering angle command for controlling a steering angle of the rear wheels of the vehicle is output to a rear wheel steering control unit, so that the oscillating motion can be suppressed.