To suppress generation of cavitation, and reduce power consumption by arranging a pump cavitation for housing an impeller which is capable of turning around a shaft, on a coolant pump of an internal combustion engine, and arranging a shaft of the impeller coaxially with a crankshaft of an engine.

A pump main body is provided with a first component 10 for forming a part of a timing case, and the crankshaft is enclosed thereby. The pump main body is provided with a cover 14 as a second component, and a circular arc shaped pump chamber (a cavity) 18 is sectioned between those components 10, 14. The cavity 18 is communicated with an inlet port 20 at one end part, and is communicated with an outlet port at the other end part. An impeller (a disk) 30 is rotatably housed in the cavity 18, and is rotated through a magnetic connection of a driven magnet 44 arranged on one side surface of the disk 30 at an equal clearance and a driving magnet 54 arranged on a pulley 46.