PURPOSE: To improve a flow velocity capable of shifting under the same current and flux densities by constituting a magnetic pole so that it is shifted in the direction of a liquid metal flow.

CONSTITUTION: Electric current flows from a positive electrode 3a to a negative electrode 3b at right angles to a liquid metal flow, and a magnetic field intersection perpendicularly to the liquid metal flow and electric current is formed by a magnetic pole 2. Accordingly, a pressure from inlet port 6 to outlet port 7 acts on said liquid metal. In this case, said magnetic pole 2 shifts while revolving in the direction of said liquid metal flow so that a relative velocity of the liquid metal to a magnetic flux decreases, a back electromotive force generated by an interaction of the liquid metal flow and magnetic flux is reduced, and lowering of discharge pressure diminishes. Thus, it is possible to improve a flow velocity capable of shifting under the same current and flux densities.