PURPOSE: To provide a proper brake force even when an openable cover is heavy in weight.

CONSTITUTION: Two hollow parts 2b and 2c partitioned from each other by means of a partition part 2a are formed in a body case 2. Pistons 3 and 4 movable along an axial direction are disposed in the hollow part 2b and 2c, respectively, the one end thereof is coupled to an arbitrary rotary shaft. Coupling members 14 and 15 for pressing and moving the pistons 3 and 4 through rotation thereof togetherwith the coupled rotary shaft are disposed. Return springs 16 and 17 capable of performing return operation of the pistons 3 and 4 to the interior of the hollow parts 2b and 2c are disposed. Further, the interior of the hollow part of each of the hollow parts 2b and 2c is separated into two liquid chambers and partition walls 5 and 6 each having an orifice, a valve hole, and a valve body are formed. Each liquid chamber is filled with viscous liquid 11 and accumulators 12 and 13 are disposed in either thereof.