A transformer core includes a first core member formed by laminating grain oriented 3% silicon steel sheets and second core members disposed at respective sides of the first core member in the direction of lamination so that the first core member is sandwiched by the second core members. Each second core member is formed by laminating non-oriented 6.5% silicon steel sheets. A commercial frequency component of magnetic fluxes mainly passes through the second core members such that an amount of noise caused by a higher harmonic component is reduced.