PURPOSE: To wind an electro-magnetic coil which does not generate short-circuit between layers by winding each layer of coil in such a manner that a coil conductor is wound along the circular cone which is concentric to the center axis of coil.

CONSTITUTION: The starting end of coil conductor 4 is arranged to the one end of the trunk part 2b of a bobbin 2 in the side of a collar 2a and is wound for the first turn. Then, winding positionis shifted by one pitch toward the other end of bobbin and the conductor is wound for the second turn. The third turn is carried out at the inclined upper side of the second turn (above the first turn) and the fourth turn is carried out above the third turn. Thereafter, the fifth turn is carried out at the inclined lower side of the fourth turn and the sixth turn is carried out at the inclined lower side (a side of the second turn). A coil 3 is wound along the circular cone having a vertical angle of as described above in such a manner that the conductor obliquely goes and return between the trunk part 2b and the collar part 2a of the bobbin and a number of turns of winding layer is increased sequentially. After an outer diameter of coil 3 reaches the specified value, a conductor is wound along the circular cone having the vertical angle of 2θ with the same number of turns for each wiring layer.