PURPOSE: To absorb a shock surely at the final time of rotatably opening a rotary lid or the like by delaying an rotary operation with a shock absorber in which a piston slides in liquid filled in a cylinder.

CONSTITUTION: When predetermined torque is applied to a rotary lid A rotated in the opening direction, the rotary lid A is successively opened against the frictional resistance due to O-rings 22, 23. Then, a ball member 54 attached to the tip of an operating rod 53 in a shock absorber 5 is moved in the direction of arrow. Since a tapered surface 41 of a cam member 4 is disposed inclined to diverge downward, the operating rod 53 is urged by the cam member 4 and slides in a cylinder 51 toward a a bottom wall 51b against a return spring 58. Since an O-ring 59 closes a groove 52b, oil 57 in the cylinder 51 moves through only an orifice 52a provided in a piston 52 to a liquid chamber at the accumulator 56 side so that the rotary lid A is opened slowly by dynamic pressure resistance and viscous resistance in the passage of the oil 57 through the orifice 52a.