PURPOSE: To improve the crack resistance and workability of a molded transformer by winding a plastic net made of fiber of specific thickness on a bobbin and main insulator and filling and immersing thermosetting resin.

CONSTITUTION: A fiber having approx. 0.1W2mm is formed, for example, of resin such as polyester, polyethylene, polyamide or the like, and a net is woven with the fiber. A plastic net 7 is wound on the center 1, a primary coil 3 is then wound, a plastic net 8 corresponding to a main insulator is then wound, a secondary coil 5 is sequentially wound, and thermosetting resin 6 is filled and hardened. Thus, resin filled with rubbery additive having excellent crack resistance and inorganic powder filling agent can be immersed without void merely by primary molding, thereby improving the quantity of its product and its workability.