PROBLEM TO BE SOLVED: To provide an element which determines easily a direction of carrier spin, in technique of quantum communication, quantum operation, etc.
SOLUTION: A first magnetic semiconductor multiple quantum well structure 2, a non-magnetic semiconductor quantum well structure 3 and a second magnetic semiconductor multiple quantum well structure 4 are formed in this order on a semiconductor substrate 1. The first well structure 2 passes carriers only in the state of down-spin and performs filtering. The second well structure 4 passes carriers only in the state of up-spin and performs filtering. The well structure 3 is irradiated with a subband light corresponding to energy between subbands, thereby determining the amount of filtered carrier, from the amount of charges flowing in the case of excitation to a second subband level.