PURPOSE: To concentrate the magnetic force generated by an electromagnet on the necessary part and to let it work efficiently by a method wherein multistaged coils, whose number of turns are changed by stage successively, are laminated and connected in series around an iron cone of a truncated cone shape, magnetic force is generated by applying DC voltage to both ends of the coils, and a magnetic-force working surface is provided on the side of the coil having the largest number of turns.

CONSTITUTION: An iron cone 1 is formed in a truncated cone shape having the diameter becoming smaller toward the lower part from the upper part, and a magnetic force working surface 2 is provided at the lower end. Multistaged coils 3 to 7 are stacked and arranged around the core 1, and between each of the 1-to-5 staged coils 3 to 7 is series-connected by a conductor 8. The ends of the first-stage coil 3 and the fifth-stage coil 7 are connected to the minus pole and the plus pole of a DC power source respectively, and when voltage is applied thereto, a fixed current is allowed to flow on the coils 3 to 7, magnetic force is generated in the direction of the center wire of the coil, namely, in the vertical direction of the core 1. As the number of turns of the coils 3 to 7 is increased in the order from the first stage to the fifth stage, intensive magnetic force is generated on the fifth stage of the coil 7, the magnetic force is concentrated on the magnetic force working surface 2 provided on the side of the coil 7, and the magnetic force works effectively.