PURPOSE: To provide a compact electromagnetic device which can continuously reduce the flowing pressure loss of a fluid and can control the flow rate and flow velocity of the fluid in the pipeline, fuel assembly, etc., of a reactor, etc., and, at the same time, can be united with a fluid element or fluid equipment in one body.

CONSTITUTION: The title device is constituted by combining a current generating means 4 and magnetic field generating means 1, 2, and 3, which are united with fluid equipment in one body. By using the means 4 and 1, 2, and 3, an electric current and magnetic field perpendicular to the flowing direction of a fluid are generated in the vicinity of a structure 5 (flow passage wall) which is in contact with the fluid. In addition, the means 4 and 1, 2, and 3 are provided so that the electric current and magnetic field can become perpendicular to each other and the force generated by the electromagnetic interaction between the electric current and magnetic field can be given to the fluid 16 in the vicinity of the structure 5 (flow passage wall).