There is providesd a nuclear magnetic resonance spectrometer having a high sensitiveness by simultaneously realizing a high uniformity of a static magnetic field and a high measuring sensitiveness. A sample tube used in the nuclear magnetic resonance spectrometer is constructed in a structure in which the shape of a sample placed in a measuring space can be changed. The change in shape of the sample can be achieved by controlling the pressure applied to the sample. There is at least one surface of contact between the sample placed in the measuring space and a gas existing around the sample, and the shape of such surface is maintained by the surface tension of the sample. In this case, a central portion of a magnet, into which the sample tube is inserted, filled with a sterilizing gas having a pressure higher than the atmospheric pressure, and the sample having a surface of contact with the gas is maintained in a sterile state. A measuring coil used in the nuclear magnetic resonance spectrometer is disposed on a rotatable curved surface symmetrical with respect to a rotational axis provided by a longitudinal center axis of the sample tube.