PURPOSE: To simplify an atomic reactor cooling system by providing an outer duct enclosing an inner duct having an inner core, an outer core having an electromagnetic coil provided on its outer periphery, and an eddy current type electromagnetic current meter provided in the inlet or outlet of the outer duct.

CONSTITUTION: An outer core 11 and an electromagnetic coil 12 are disposed on the outer periphery of an outer duct 10, an inner duct 14 containing an inner core 13 is disposed at a position axially opposite to the core 11 inside the duct 10, and an annular liquid metal passage is formed to the duct 10. An eddy current type electromagnetic current meter 15 is disposed at the center of the passage at a predetermined distance from the core 11 and the coil 12. Since it is rectified by the duct 10, the flow rate can be measured by measuring the flowing velocity at the center of the duct 14 to simplify the system configuration, thereby increasing the degree of freedoms of designing the disposition.