A magnetic device includes: a magnetoresistive effect element having a magnetization fixed layer, a magnetization free layer, and a nonmagnetic layer sandwiched between the magnetization fixed layer and the magnetization free layer; an input terminal for feeding an AC signal to the magnetoresistive effect element in its stacking direction; and an output terminal for extracting an output voltage from the magnetoresistive effect element, wherein the nomagnetic layer includes an insulating layer portion comprising an insulating material, and a current-constricting layer portion comprising a conductive material which passes through the insulating layer portion in its film thickness direction.