To provide a laminated balun transformer that is reduced in size, particularly, in thickness.

This laminated balun transformer is composed of a first strip line 21, having first and second conductors 22a and 22b and provided on one main surface of a dielectric substrate 12c, a second strip line 23 which is provided on the other main surface of the substrate 12 to face the first conductor 22a, and a third strip line 24 faced to the second conductor 22b via the substrate 12c. The transformer is also composed of a grounding electrode 16, which faces the first strip line 21 via the substrate 12b and to which one ends of the first and second conductors 22a and 22b are connected via the substrate 12c.