PURPOSE: To increase pressure delivered by a pump and its delivering capacity by providing a means for pressuring inside of a pump bellows from inside, in a bellows pump in which a central driving portion alternately operates a pair of delivering portions arranged on its both sides.

CONSTITUTION: In this double-acting bellows pump 10 having a central driving portion 11 and delivering portions 12, 12' arranged on its both sides, the central driving portion 11 is constituted by providing a driving piston 15 in a housing portion 13. The delivering portions 12, 12' are alternately operated by controlling charge/discharge of fluid for pressure chambers 16, 16' partitioned on the both sides of this driving piston 15 by means of a valve assembly 18. The delivering portion 12 (12') is constituted by providing a delivery bellows 31 in a pressure chamber of a pump head 22, and is linked with the end of a piston rod 21. The delivery bellows 31 is integrally formed from plastic material, and a plurality of annular coils 44 positioned adjacently to the axial direction are provided on an axially contractible sleeve-shaped side wall 34.