A spin transport device includes a semiconductor layer 3, a first ferromagnetic layer 1 provided on the semiconductor layer 3 via a first tunnel barrier layer 5A, and a second ferromagnetic layer 2 provided on the semiconductor layer 3 via a second tunnel barrier layer 5B to be spaced from the first ferromagnetic layer 1, and the semiconductor layer 3 includes a first region RI broadening in a direction away from the first ferromagnetic layer 1 along a direction orthogonal to a thickness direction from the first ferromagnetic layer 1, and a second region R12 extending in a direction toward the second ferromagnetic layer 2 along the direction orthogonal to the thickness direction from the first ferromagnetic layer 1. The second region R12 has a relatively higher impurity concentration than the first region R1.