Microwave generating and detection portions of a electronic circuit is improved in efficiency and reduced in size. A microwave generating element A comprises a lower electrode 1, a layer 3 formed on the lower electrode 1 in an island shape, forming a magnetoresistance element, an insulator 7 formed on the lower electrode 1 in such a manner as to surround the layer 3 forming the magnetoresistance element, and an upper electrode 5 formed on the insulator 7 and the layer 3 forming the magnetoresistance element. The layer 3 forming the magnetoresistance element includes, in order from the side of the lower electrode 1, a magnetization fixed layer 3a, an intermediate layer 3b, and a magnetization free layer 3c. The magnetization free layer 3c, which is required to produce resonance oscillation based on a current, preferably is dimensioned to be equal to or smaller than 200 nm square in a cross-sectional area and on the order of 1 to 5 nm in film thickness, for example. The magnetization fixed layer 3a, when made of a single material, is required to have a thickness 10 times or more of the thickness of the magnetization free layer 3c. The magnetization fixed layer 3a may be comprised of a magnetic metal multilayer film that utilizes antiferromagnetic coupling.