A spin transistor according to an embodiment includes: a first magnetic layer formed above a substrate and serving as one of a source and a drain; an insulating film having a lower face facing to an upper face of the first magnetic layer, an upper face opposed to the lower face, and a side face different from the lower and upper faces, the insulating film being formed on the upper face of the first magnetic layer and serving as a channel; a second magnetic layer formed on the upper face of the insulating film and serving as the other one of the source and the drain; a gate electrode formed along the side face of the insulating film; and a gate insulating film located between the gate electrode and the side face of the insulating film.