To provide the water hammer prevention device of a check valve capable of preventing the water hammer action effectively by simple structure.

A retainer pipe 15 of both ends opening is arranged into a short pipe 7 forming the annular space 16 with a short pipe and an elastic tube 18 is arranged on an outer circumference to cover the opening while forming an opening 17 on the retainer pipe. Besides the annular space 16 communicates with a flow channel 3 on the upstream side of the valve body and a part of flow accepts an elastic tube 18 so as to swell it to the side of the annular space 16 from the opening 17 when flowing backward, it is composed so that the communicating channels 27, 35, 36, 37 to distribute a part of flow in the annular space 16 to the channel 3 on the upstream side of valve body are formed between the short pipe 7 and the valve body holder 2.