To solve such a problem that an already known surge suppressing device is enlarged while holding an advantage of the surge suppressing device.

In the surge suppressing device including a housing and a soft diaphragm, and wherein the housing is divided into first and second sub- chambers by the diaphragm, the first sub-chamber has a connecting means for connecting the first sub-chamber to a supplying source for a pressurized liquid, and the second sub-chamber includes pressurized gas; the surge suppressing device includes a gas reservoir communicated with the second sub- chamber so as to provide an effective capacity larger than that of the second sub-chamber in the case of use.