PURPOSE: To attain reading of the bar code with a high read rate by forming a narrow slot adjacent to a wider slot wider than another narrow slot not adjacent to the said wider slot.

CONSTITUTION: The width l1 of a narrow slot 3 adjacent to a wider slot 2 is formed wider than the width l2 of another narrow slot 4 not adjacent to the said wider slot 2. Thus, the interval of extreme values of the horizontal component of magnetic flux density corresponding to the narrow slot 3 adjacent to the wider slot 2 is wider and the width l1 of the slot 3 is selected to be 120% of the width l2 of the slot 4, then the interval of extreme values of the horizontal component of the magnetic flux density corresponding to the slot 3 is nearly the same as that of the slot 4 and a high read rate is attained. Moreover, a projection 5 clipped by the wider slot 2 and the narrower slot 3 is made narrower by the widened narrow slot 3 adjacent to the wider slot 2 to keep the entire length the same as a conventional code.