PURPOSE: To prevent the stagnation or the reverse flow of electroconductive fluid and improve reliability as well as efficiency by a method wherein shielding blocks, made of an electroconductive material, are provided in an annular flow passage between core blocks, in which discharging pressure is small.

CONSTITUTION: A solenoid pump is provided with an outside tube 4 and an inside tube 5. An external stator core 1 is arranged on the outside of the outside tube 4 while a stator coil 2 for obtaining an axial travelling field in a duct is arranged in the duct of the external stator core 1. Further, shielding blocks 11, made of an electroconductive material, are arranged in an annular channel 3 between the core blocks of said tubes 4, 5. In this case, a pressure deterioration in the flow passage between the blocks of the cores 1, 6, in which a flux density is low, does not generate the flow of the fluid since there are the shielding blocks 11 whereby it does not affect to the whole of the flow and, therefore, the flow is stabilized. On the other hand, reverse flow will never be generated when slip S is large and, therefore, the discharging pressure in the flow passage may become high as a whole and the efficiency of the title pump may be improved.