The present invention provides a bellows pump that is capable of reliably preventing deformation of the bottom wall of a bellows due to pressure fluctuations in the pump chamber and that can achieve proper pump functionality, providing stable flow rates and circulating-fluid volumes. The bellows pump is configured as follows: plastic bellows (6) expand and contract in the axial direction to alternatively execute an output stroke that sends fluid out of pump chambers (7) defined by the bellows (6) and a suction stroke that supplies fluid to the pump chambers (7). Metal actuation plates (10) are supported in the pump case (5) so as to be movable in the axial direction. Said actuation plates (10) are fixedly connected to the bottom walls (6c) of the bellows (6) in peripheral portions thereof. A central portion of the bottom walls (6c) of the bellows (6), i.e., a fluid-contact portion (6f) in contact with the fluid in the pump chamber (7), is in close contact with opposed end faces (6g, 10c) of the actuation plates (10), and the close-contact portions (6g, 10c) are sealed with O-rings (15) sealing member.