PURPOSE: To obtain an apparatus for measuring Si concentration or electromagnetic characteristics equipped with a detecting means which can easily follow up movement of material to be measured, occurrence of slip, abrupt speed change or snaking.

CONSTITUTION: The apparatus comprises a contact-type detecting means 5 equipped with at least a pair of conduction electrode and voltage measuring electrode, means 20 for elevating/lowering the detecting means 5, a first drive means 22 for driving the detecting means 5 to follow up the movement of a material 1 to be measured, a second drive means 33 for moving the detecting means 5 in breadthwise direction of the material 1, and a speed control means 26 receiving a signal from a noncontact speed detecting means 31 for detecting the moving speed of the material 1 and delivering a control signal to the first drive means 22. The apparatus further comprises a breadthwise position control means 36 receiving a signal from means 34 for detecting breadthwise position of the material 1 and delivering a control signal to the second drive means 33, and means 30 for measuring Si concentration or electromagnetic characteristics of the material 1 based, on the output signal from the detecting means 5.