A rectangular coil unit is manufactured in such a manner that two wires are simultaneously regularly wound on four outer surfaces of a bobbin having a rectangular section so that the wires 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 and for a lane change corresponding to 1.5 wires on the other one (an upper surface side) of the parallel surfaces.