In the IR (Inversion Recovery) method, to observe a phenomenon in which a nuclear spin returns to a steady state, a 90-degree pulse is irradiated after a lapse of time .tau. after finishing applying a 180-degree pulse. An FID signal starts being processed after a lapse of reception delay time Dd after finishing applying the 90-degree pulse. Among the FID signals from protons in a plurality of environments in a solid sample, an FID signal high in time-dependent attenuation rate almost disappears during the lapse of reception delay time Dd. Therefore, an FID signal of a proton in an environment intended to be measured can be easily selected and extracted from FID signals of other protons.