To inhibit the dispersion of characteristics such as an inductance value in a transmission transformer in which a permalloy or the like is applied to a magnetic core (a laminated core).

The transmission transformer 6 has a bobbin 1 on which a winding is wound, and the magnetic core 5 composed of a plurality of magnetic alloy pieces 4 incorporated into the bobbin 1 such as ones 4 consisting of the permalloy. A plurality of the magnetic alloy pieces 4 have deflection X respectively, and laminated by arranging the direction of deflection X. The deflection X of each magnetic alloy piece 4 is set so that the quantities of deflection to the length of one side of the magnetic alloy pieces 4 is kept within a range of 2-20%.