A fluid mixer which can mix fluid while making the distribution of concentration or distribution of temperature of the fluid in the direction of flow uniform without any unevenness and which is both compact and easy to install piping for is provided. Thus, the infusion pump system can draw upon the energy supply in an efficient manner that extends the useful life on the power supply. The invention further relates to derivatives of the oligomers and oligomers based on abbreviated forms of the amyloid-\u03b2 proteins, the production and use thereof. The copolymer is excellent in antithrombotic activity and further in biocompatibility and can be used as a medial material having high hydrophilicity.