The magnetoresistance effect device includes: a magnetoresistance effect element that includes a first magnetization free layer, a magnetization fixed layer or a second magnetization free layer, and a spacer layer interposed between the first magnetization free layer and the magnetization fixed layer or the second magnetization free layer; and a magnetic material part that applies a magnetic field to the magnetoresistance effect element, wherein the magnetic material part is arranged to surround an outer circumference of the magnetoresistance effect element in a plan view in a stacking direction L of the magnetoresistance effect element.