To provide a bellows pump dealing with explosive gas or the like as a pump transport fluid, which materializes miniaturization and a high level of safety while preventing danger that the leaked pump transport fluid due to breakage of the bellows enters a driving part of a drive motor or the like.

A flexible diaphragm (22) is stretched between the movable end (8b) of a bellows (8) and a pump housing (6) to take an area (23) outside the bellows as a sealed chamber. The flexible diaphragm follows reciprocation of the bellows not to cause any trouble with the operation. Even if pump transport fluid leaks out of a pump chamber 11 due to breakage of the bellows during pump operation, leaked fluid is retained in the area outside the bellows so as not to reach a driving part including a drive motor (14). The flexible diaphragm prevents entry of trash and dust or the like to the bellows side from the outside. In addition, the resulting malfunction such as breakage of the bellows can be prevented.