To obtain a soft magnetic thin film having improved soft magnetic characteristics, thermal stability and corrosion resistance, this invention uses a soft magnetic thin film comprising Fe as the principal component thereof and containing Ta and/or Hf and C and/or N, wherein the (110) plane of Fe is preferentially oriented, the size d.sub.1 of the Fe crystal particle is not greater than 15 nm and the size d.sub.2 of the Ta--C, Ta--N, Hf--C or Hf--N particle is not greater than 3 nm. The crystal particle size is controlled by causing first the Fe crystal particle to precipitate at the initial stage of the film formation and then causing the crystal particle of Ta--C, Ta--N, Hf--C or Hf--N to precipitate.