DIAPHRAGM PUMP

A diaphragm pump is provided in which, when a rolling diaphragm is set to an extended attitude by projectively moving a piston as far as possible, a curved portion that is formed by opening a folded portion does not have a distorted shape, but has an expected shape that is smoothly curved, whereby the liquid quantity and time period that are required for a liquid replacement in a flushing mode can be reduced, and the liquid replacement efficiency is improved. In a diaphragm pump having: a fluorine resin-made rolling diaphragm 3 including: an inner circumferential portion 3c which elongates along an outer circumferential surface 2e of a piston 2; an outer circumferential portion 3e which elongates along the inner circumferential surface 1r of a cylinder 1; and a folded portion 3d which is formed by folding back in a tubular space 13 between the cylinder 1 and the piston 2; and a pump chamber 4 which is separated by the rolling diaphragm 3 in the cylinder 1, the rolling diaphragm 3 is produced in an extended attitude corresponding to an attitude obtained when, by a projective movement of the piston 2, the outer circumferential portion 3e is eliminated, and the folding of the folded portion 3d is opened.