Abstract: A water hammer absorber provided in a cold or hot water supply passage including: a tubular portion whose cross section gradually decreases toward a flow direction of cold or hot water until the inner diameter of the portion becomes minimum and then gradually increases toward that direction so that a negative pressure generates therein; and a pressure absorbing chamber which is formed at the minimum inner diametered section of the tubular portion or therearound at the downstream side so as to communicate with the water supply passage and which is provided with a passage-way leading to the atmosphere and a check valve disposed in the passage-way and capable of admitting the entry of air only into the pressure absorbing chamber. The absorber according to the invention is suitably used in the joint of a delivery faucet or a mixing faucet.