To provide a balun transformer which can be made compact and can improve insertion loss by optimizing the electromagnetic coupling of strip lines.

This standard balun transformer 11 is provided with a dielectric layer 12c where a spiral strip line 33 is formed, a dielectric layer 12b where a spiral strip line 32 is formed, a dielectric layer 12a where a spiral strip line 31 is formed, and a dielectric layer 12e where an earth electrode 40 is formed. The dielectric layers 12a and 12e are stacked in the transformer 11. In this case, the dielectric layer 12a and 12b are formed adjacent to each other.