A rectangular coil unit 1 is manufactured in such a manner that four wires 2 are simultaneously regularly wound on four outer surfaces of a bobbin 3 having a rectangular section so that the wires 2 advance obliquely together for a lane change corresponding to 0.5 wire on one (a lower surface side) of a pair of parallel surfaces of the four outer surfaces of the bobbin 3 and for a lane change corresponding to 3.5 wires on the other one (an upper surface side) of the parallel surfaces.