PURPOSE: To easily form a uniform high gradient magnetic field, by simple constitution such that ferromagnetic wires are embedded and fixed at upper, lower, left and right positions of a separation groove in parallel to said separation groove.

CONSTITUTION: Ferromagnetic wires 2W5 are parallelly arranged at the left, right, upper and lower positions of a separation groove 1 along the flow passage thereof and a uniform magnetic field Ho is applied in the direction at a right angle to said wires 2W5. By this method, a high gradient magnetic field highest at the center of the cross-section of the separation groove 1 and becoming gradually low from the highest part to the longitudinal direction is formed. Therefore, the movement of a solute generates along the longitudinal direction of the cross-section of the separation groove and the separation of the solute is enabled.