Provided are a method and device for improving a response speed in a measurement of viscosity of a fluid and obtaining a continuous smooth measurement graph. A viscometer includes a machine part that generates a shear rate in a sample, a machine drive, a shear rate changing means that outputs a target shear rate of the machine part, and a displacement detection sensor that measures displacement of the machine part, and performs feedback control to control a driving force of the machine drive so that an output value of the displacement detection sensor corresponds to the target shear rate and measures a viscosity of a sample, wherein a feedback gain is simply set for each measurement according to an optimum design or target shear rate.