The present invention makes it possible to measure a plurality of samples under a certain concentration condition of the small molecule by the circulation transfer of a small molecule solution through a small molecule concentration control portion for injecting, discharging or feeding the small molecule solution, a mixing filter portion for mixing a solution (sample) containing the large molecule sample with the small molecule solution, a container set in a nuclear magnetic resonance probe, a separating filter portion for separating the mixture into the sample and the small molecule solution, and the small molecule concentration control portion; injecting the sample from the mixing filter portion; holding the sample in a measurement portion in the container; and discharging the sample from the separating filter portion after completion of the NMR measurement.