To automatically compensate for force to be changed, in particular, reaction force to be generated on a diaphragm by a discharging medium, by improvising a diaphragm pump.

A ring-shaped hollow chamber 9 coaxial with a rotational axis 8 is housed in a casing 10 to be rotated together, at least two roller members 12 are arranged in the hollow housing, the hollow members are freely rolled on the inner surface 13 of the outer peripheral part of the hollow chamber, there is no liquid inside the hollow chamber besides the roller members, and the width in the radial direction of the hollow chamber 9 exceeds a little the diameter in the radial direction of the roller members 12. The roller members 12 can be reciprocated between the limiting part outside the hollow chamber 9 and the limiting part inside it, and therefore, the roller members 12 can be entrained in the circumferential direction in starting on the basis of the sliding friction between the roller members 12 and between the limiting parts in the radial direction of the ring-shaped hollow chamber 9.