PURPOSE: To provide an annealing method with which embrittlement can be suppressed when an amorphous core is annealed, and also excellent iron loss and excitation capacitance can be obtained.

CONSTITUTION: An amorphous iron core is formed using the amorphous material which is excitation-annealed in a nitrogen atmosphere at 300 to 335°C for 120 hours or longer. Accordingly, the embrittlement of the amorphous iron core can be suppressed, and excellent characteristics in iron loss and excitation capacitance can be obtained.