To provide a rotary damper which can be miniaturized and lightened, and also in which arm installation work to a rotary shaft is facilitated without increasing the number of part items.

In this rotary damper in which a pressure chamber filled with fluid is formed among a easing 1 and both side plates 3, 3 arranged to be relatively rotated in the inside of the easing 1 and an extension side disk valve and a compression side disk valve generating required damping force to relative rotation among the casing 1, both the side plates 3, 3 and rotary vanes are arranged in a first communicating passage mutually communicating pressure chambers partitioned by the swinging vanes rotated integrally with both the side plates 3, 3, both the end flat surface parts of both the side plates 3, 3 are projected in a shaft direction from both the end surfaces of the easing 1 so as to be formed into a flat surface part to be connected to an upper link arm 30.