PURPOSE: To obtain the instrument capable of performing two different kinds of measurement as magnetic domain observation and magnetization measurement in a short time by utilizing the Kerr effect.

CONSTITUTION: This is a microscopic device for detecting a magnetic domain pattern of a magnetic substance as to be light and shade corresponding to the size of magnetization and a difference in its direction by the longitudinal Kerr effect with polarized light. The device is equipped with a CCD camera 2 and a light oscilloscope 4 as detectors, and is also equipped with a rotatable mirror 1 between the CCD camera 2 and a head 3 of the light oscilloscope, where by making the light to be detected by changing the angle of the mirror 1 incident upon either the CCD camera 2 or the head 3 of the light oscilloscope, the magnetic domain observation and magnetization measurement is carried out in a short changeover time.