PURPOSE: To optionally vary operating torque.

CONSTITUTION: A rotary shaft 1 and an adjusting shaft 4 for load torque have ≥1 disk members 3 and semicircular members 7 fixed at certain intervals, and are supported rotatably in a container 2 which is filled with viscous liquid 8. When the adjusting shaft 4 is rotated and fixed at a position where orthogonal projections of the disk members 3 and semicircular members 7 overlap with each other, the load torque when the rotary shaft 1 is rotated is affected by not only the viscous frictional force between the disk members 3 and viscous liquid 8, but also the viscous frictional force between the semicircular members 7 and viscous liquid 8. The viscous frictional force increases with the area of the semicircular members 7 that are present in a flow, so the load torque of the rotary shaft 1 can be varied by varying the overlap area between both the members through the rotation of the adjusting shaft 4.