To provide a pump whose elastic member has long life, a pump according to an embodiment of the invention comprises an inner wall surface having a cylindrical shape, an elastic ring disposed along the inner wall surface and forming an operation chamber extending in a circumferential direction of the elastic ring with respect to the inner wall surface, and a plurality of pressing members pressing a part of the elastic ring in the circumferential direction against the inner wall surface and thereby forming a blocking part in the operation chamber, wherein the plurality of pressing members cause fluid in the operation chamber to move by rotating along the inner wall surface and thereby moving the blocking part, and the elastic ring is disposed to maintain a circumference in a natural state of the elastic ring.