In an NMR apparatus provided with a split type magnet, in order to position a probe at a high precision in a narrow homogeneous magnetic field space, a positioning of a center of a probe coil is first located to a proper position by inserting an NMR probe from a horizontal bore. At this position, a sample tube is inserted from a vertical bore, and an NMR signal is measured from the probe coil. An NMR signal measuring apparatus amplifies the NMR signal from the probe coil, and executes an A/D conversion so as to determine an NMR spectrum signal, and an NMR signal analyzing apparatus compares the NMR spectrum signal. A probe is set at a position where a sharpness of the spectrum is largest, that is, a magnetic field homogeneity coefficient is high, by repeating the operations mentioned above.