PURPOSE: To enable easy grasping of damage of a bellows, by a method wherein the surroundings of the bellows of a bellows pump are covered with closing covers, exhaust air from an air cylinder for driving is caused to flow in the closed cover, and leak fluid, mixed in the exhaust air, is detected.

CONSTITUTION: Surroundings of bellows 2 and 3 of a bellows pump 1 are covered with closing covers 15 and 16, and meanwhile, an air cylinder 11 for driving a bellow pump is mounted to the end part of the one closing cover 15. Air inlets 19 and 20, through which exhaust air from the air cylinder 11 is introduced, and air outlets 21 and 22, through which air flowing through the closing covers 15 and 16 is exhausted, are formed in a part of the closing covers 15 and 16. Thus, mounting of detectors 27 and 28, detecting working fluid in a bellows pump in exhaust pipes 25 and 26 connected to the air outlets 21 and 22 enables rapid detection of leak of fluid due to damage occurring to the bellows 2 and 3.