To attain relatively high efficiency both in high-rpm drive range and in high-torque drive range, by laminating steel plates of high permeability and low magnetic flux density and steel plates of low permeability and high magnetic flux density in specified proportions to form the iron core of an electric rotating machine.

An outer core 10 is formed by laminating two types of steel plates: first steel plates 12 and second steel plates 14. The first steel plates 12 are formed of a material high in permeability and low in saturation magnetic flux density (high- permeability, low-magnetic flux density material), and the second steel plates 14 are formed of a material which is low in permeability and high in saturation magnetic flux density (low-permeability, high-magnetic flux density material). Examples of the high-permeability, low-magnetic flux density material include sendust and electromagnetic steel plates obtained by adding silicon or aluminum to iron, and 80% Ni-Fe (Permalloy (R)). Examples of low-permeability, high-magnetic flux density material include Fe- 50%Co (Permendur (R)) and pure iron. The properties of the material can be brought only when it is close to those of the first steel plates 12 or second steel plates 14, only when appropriately selecting the volumetric ratio of the first and second steel plates 12 and 14.