A first magnetostrictive member 1a is housed in a storage section 2f of a first frame 2a and a second magnetostrictive member 1b is housed in a storage section 2g of a second frame 2b. They are fixed by an adhesive, etc., so as to sandwich a belt-like magnetic member 3 between the frames 2a and 2b. A sealing plate 4a, 4b is fixed to the opposite side of the frame 2a, 2b, forming a magnetostrictive resonator 5. When an electromagnetic wave is applied from the long side direction of the magnetostrictive member 1a, 1b, a magnetic field is applied to the magnetostrictive members 1a and 1b. When the frequency matches the resonance frequency of the magnetostrictive member, the magnetostrictive resonator 5 vibrates with the maximum amplitude. An electromagnetic wave emitted from the magnetostrictive member 1a or 1b can be detected based on mechanical vibration continuing for a short time still after the magnetic field is stopped. IMAGE
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