PURPOSE: To obtain the magnetic scanning method and device, which detects the streak in a silicon steel piece, wherein crystal grains are oriented, and the difference in magnitude and streaks of the crystal grains and the mixed grains, and identifies the difference.

CONSTITUTION: The crystal-grain structure of an electric steel piece S is tested by exciting the magnetic flux in the steel piece by pole pieces 39 and 40 at both sides of a permanent magnet. When the detecting head of the steel piece or magnetic flux is relatively moved, a magnetic detector head 35 between the pole pieces responds to the leakage of the magnetic flux. A recorder, which identifies the mixed crystal-grain structure for decreasing the leakage of the magnetic flux than larger intended crystal grains and the streaks, is used.