An instrument locally measuring mobility of a protic solvent in a sample 115 based on the gradient magnetic field NMR method has a sample stage 116 on which the sample 115 is placed, a magnet 113 applying a static magnetic field to the sample 115, a G coil 151 and a G coil 153 applying a gradient magnetic field to the sample 115, a small-sized RF coil 114 smaller in size than the G coil 151 applying an oscillating magnetic field for excitation and acquiring an NMR signal corresponded to the oscillating magnetic field for excitation and the gradient magnetic field; a pulse control unit 108 alloing application of the gradient magnetic field and oscillating magnetic field for excitation to be executed according to a predetermined pulse sequence; and an operation unit 130 calculating the mobility at the specific position of the G coil 151, based on information of the NMR signals acquired corresponding to different gradient magnetic fields.