PURPOSE: To eliminate limitations on the selection of a viscometer and use an inexpensive viscometer by constituting a measurement cell in double-tube structure and making the top surface of the internal tube open in the external tube.

CONSTITUTION: The measurement cell 2 is constituted in the double-tube structure consisting of the internal tube 21 and external tube 22. Further, the top surface of the internal tube 21 is made open in the external tube 22 and a solution which is pumped up from a solution tank 1 by a pump 4 for circulation provided to a solution supply pipe 11 flows in the internal tube 21 from its bottom surface and then flows in the external tube 22 by overflowing the open part of the top surface. The sensor of the viscometer 3 is provided in the solution in the internal tube 21 to measure the viscosity. Further, the solution which overflows from the internal tube 21 and flows in the external tube 22 enters an in-use device from the bottom part of the external tube 22 through an intake pipe 12. Thus, the solution overflows from the internal tube 21 by a stationary constant amount, so pulsation due to the pump 4 for circulation, etc., is eliminated to smoothly circulate and supply the solution.