PUMP UNIT

PROBLEM TO BE SOLVED: To provide a pump unit with an inner cylinder, the pump unit having superior durability, facilitating manufacture, and having less variations in manufacturing the same.SOLUTION: A pump unit includes an outer cylinder, an inner cylinder comprising a rubber member arranged in the inner peripheral side of the outer cylinder, fixing members for fixing both ends of the inner cylinder in an axial direction and both ends of the outer cylinder in the axial direction, and a passage for pressurizing for supplying a medium for pressurizing between the outer cylinder and the inner cylinder, conveys a fluid by expanding the inner cylinder by the medium for pressurizing, wherein a plurality of rubber deformed parts extending from one side to the other side of the inner cylinder in the axial direction along a peripheral face and inducing a folding line in the inner cylinder by a pressure of the introduced medium for pressurizing are arranged in the peripheral direction of the inner cylinder, in the inner cylinder.