Electron spin resonance device and deterioration evaluation method

An electron spin resonance device comprising a microwave oscillator, a magnet, a modulation coil, and a cavity resonator having an opening, wherein

• a microwave generated by the microwave oscillator resonates in the cavity resonator and is emitted from the opening toward a measurement target located outside the opening,
• the magnet applies a magnetic field toward an irradiation surface of the measurement target, the irradiation surface being irradiated with the microwave,
• the modulation coil modulates an intensity of the magnetic field or a frequency of the microwave applied toward the irradiation surface of the measurement target,
• the measurement target includes 1011 spins/g or more in a permeation region which is irradiated and permeated by the microwave, and
• the microwave oscillator and the magnet are located at a position facing the measurement target and do not sandwich the measurement target.