Drive-force distribution controller and drive-force distribution method for four-wheel-drive vehicle

A drive-force distribution controller controls a drive-force transmission apparatus (17) of a vehicle in order to control transmission of drive force to rear wheels (20) or front wheels (16) of the vehicle in accordance with a designated drive-force transmission ratio. The drive-force transmission ratio is changed on the basis of vehicle speed, differential rotational speed (speed difference between the front and rear wheels), and throttle opening. Alternatively, the drive-force transmission ratio is changed on the basis of vehicle speed, throttle opening, and throttle open speed. The change speed of current which is supplied to the drive-force transmission apparatus in order to control the drive-force transmission ratio is adjusted in accordance with a command current filter value which is determined on the basis of vehicle speed and a command current filter map of a vehicle-speed responsive type.