PURPOSE: To provide a titled improving device for magnetic characteristics which provides improved productivity by providing an optical system which generates alternately pulse laser light from twi units of laser oscillators, and scans and irradiates the surface of a steel sheet at a specific oscillation frequency.

CONSTITUTION: Pulses of an oscillation frequency 2f are oscillated from a master synchronizing pulse circuit 5, and the pulses are alternately used to trigger laser devices 2 and 2'. The laser light of a frequency (f) are oscillated from the devices 2, 2' according to the trigger pulses. The laser light is respectively split by a beam splitter 6 and the one of the transmitted and reflected laser light is made incident to a scanner S. The other is made incident to a scanner S' via a reflecting mirror 7. A steel sheet 1 is thus scanned by the pulses of the frequency 2f at a width w.