Abstract: A rotary viscometer has a control mode for measuring the viscosity of a liquid sample with a high viscosity or a high yield value in an ultra-low shear rate range using a spring relaxation method. In this rotary viscometer, a pivot protecting device attains a locked state in which a pivot is separated from a bearing and a rotor shaft is locked against the rotation therein, a released state in which the lock of the rotor shaft is released while the pivot is in contact with the bearing, and a latched state disposed therebetween, in which the rotation of the rotor shaft is locked and the pivot is in contact with the bearing. Responding to user's instructions, a control device controls a locking motor to bring the pivot protecting device to a designated state, and controls a rotational driving motor in accordance with the state. For the spring relaxation measurement, the control device controls so that the spring is wound up while the pivot protecting device is in the latched state.