Continuous high-frequency waves and pulse-like high-frequency waves of the same frequency are selectively applied to a specimen placed in a unidirectional magnetic field, whereby resonance signals and free induction decay signals are selectively produced by the specimen. These signals are detected, and the detected free induction decay signals are Fourier-transformed, so that the continuous wave nuclear gyromagnetic resonance and the Fourier-transformed nuclear gyromagnetic resonance can be selectively measured.