To prevent backflow (partial backflow) at both discharge and suction sides from occurring as well as to reduce the pulsation.

A pump tube is installed in space between a guideway 10 formed on an inner surface of a casing 1 and a roller 4 to be rotated with a pump shaft 2 as the center, and both diametral contraction and expansion operations of the pump tube are repeated according to a rotation of the roller 4. This guideway 10 is divided into three areas, a suction side buffer part 12 formed from the suction side to the discharge side in order without any level difference with each other, an intermediate roundness part 13 made into complete round form centering on the pump shaft 2, and a discharge side buffer part 14, respectively. In this constitution, the suction side buffer part 12 is formed as a curve of more than the secondary degree so as to make the roller 4 gradually contact with the pump tube, and the discharge side buffer part 14 is formed as a curve of more than the secondary degree so as to make the roller 4 gradually separate from the pump tube.