PURPOSE: To attain braking force according to vibration amplitude with a simple means by composing a first and second liquid discharge chambers respectively of two coupling halves arranged in an inner chamber, a hanging braking ring which is rotated a constant rate relatively therewith.

CONSTITUTION: A first coupling half is composed of side plates 7, 8 surrounding a second coupling half 2 and forming an airtight chamber 11. Torque is transmitted through a spring 9 housed in corresponding recessions 10 on a center plate 6 or the side plates 7, 8. A hanging braking ring 50 is arranged between the center plate 6 and an outer peripheral part 13 of the inner chamber 11. A first liquid discharge chamber 16 is formed by the first coupling half 1 and a bolt 12, while a second liquid discharge chamber 17 is formed by the first coupling half 1 and the center plate 6. A cam 51 and a projection 53 are formed on outer and inner peripheral parts. The liquid discharge chambers 16, 17 have different braking characteristics from each other. The coupling reacts to twisting vibration with braking force according to vibration amplitude with a simple means for attaining calm running.