A bellows that is extendingly and contractingly deformable in the axial direction is placed in a pump body and forms a liquid chamber inside the bellows. A suction portion and a discharge portion are formed in an inner bottom face of the pump body facing the liquid chamber. Liquid is sucked from the suction port into the liquid chamber by extension of the bellows, and the liquid in the liquid chamber is discharged from the discharge portion by contraction of the bellows. The extending and contracting portion of the bellows which is configured by forming ridge-like folds and valley-like folds in a vertically alternate and continuous manner is formed into a shape in which the lower one of upper and lower lamella portions of each of the ridge-like folds, or the lower lamella portion is inclined downwardly toward the axis defining the axial direction, not only in an extending state but also in a contracting state. Even in the case where liquid containing a sedimenting material such as slurry is used, therefore, the sedimenting material can be prevented from sedimenting and stagnating in the extending and contracting portion of the bellows.