An spin-injection FET includes a first ferromagnetic body whose magnetization direction is fixed, a second ferromagnetic body whose magnetization direction is changed by spin-injection current, a gate electrode which is formed on a channel between the first and second ferromagnetic bodies, a first driver/sinker which controls a direction of the spin-injection current to determine the magnetization direction of the second ferromagnetic body, the spin-injection current being passed through the channel, a wiring through which assist current is passed, the assist current generating a magnetic field in a magnetization easy axis direction of the second ferromagnetic body, and a second driver/sinker which controls the direction of the assist current passed through the conductive line.