The present invention relates to a simple and small cylinder pump, which can stably supply a medical fluid regardless of the installed height of a liquid container or a blood bag. The cylinder pump includes an upper casing, and a lower casing coupled to the upper casing. An upper rotation member is rotatably inserted in the upper casing. A lower rotation member slidingly contacting the upper rotation member is rotatably inserted in the lower casing. An inner wall of the upper casing, a lower outer surface of the upper rotation member, an inner wall of the lower casing, and an upper outer surface of the rotation member constitute a cylinder having a single-tube shape. Plungers are installed on the upper rotation member and on the lower rotation member, respectively, and rotate in the cylinder, the ends of which are closed.