PROBLEM TO BE SOLVED: To make exchangeable samples while keeping a cell in a set position and to make mixable a plurality of samplers under a high pressure.
SOLUTION: An NMR cell for use in the NMR measurement of supercritical fluid has a capillary 4 with an end extended to near a bottom. A cell holder 3 provided with the connections of an inlet 1 and an outlet 2 has the capillary 4 connected to one of the connections to form a flow type cell 5. Samples can be exchanged without removal of the cell 5. The capillary 4 has a plug part integrated therewith which forms a fluid sump near the bottom within the cell 5 and closes the top. The fluid sump is communicated with the other of the connections via a clearance between the outer peripheral surface of the plug part and the inner peripheral surface of the cell to reduce a temperature gradient within a measuring sample system to inhibit convection. A pressurizer and a pressure regulator are connected respectively to the inlet and the outlet of the cell holder to enable the samples to be exchanged and mixed.