A flexible tube has a first portion and a second portion located close to each other in the vicinity of an opening of an accommodating case. A pressing member moves from the first portion to the second portion along the tube while pressing a portion of the tube. An assistant member is provided in the vicinity of the opening of the case. The assistant member has an assistant surface. When the pressing member passes the vicinity of the opening of the case, the assistant member transfers the pressing member from the second portion to the first portion via the assistant surface. This structure ensures a silent operation of the tube pump.