PURPOSE: To measure the tension of a metal strip in a non-contacting state irrespective of the kind of the material of the plate by simultaneously or successively spraying a fluid upon a plurality of locations in the width direction of the strip and detecting microdisplacement generated in the strip.

CONSTITUTION: A metal strip 9 drawn out from a coil by means of a drawing- out means 1 is wound into a coil by means of a winding means 3 after the strip 9 is rolled with rollers 2. Fluid spraying means 4 are installed to a plurality of locations in the width direction of the running strip 9. While a liquid or gas can be used for the fluid when the liquid or gas is harmless to the metal of the strip, compressed air is preferable. Microdisplacement generated in the strip 9 due to the sprayed fluid is detected by means of a displacement sensor 5, such as an eddy-current displacement gauge, etc. A computing element 6 calculates the tension of the strip 9 based on the detected displacement and a controller 7 controls the drawing-down of the strip 9 by tilting the roll 2 in the width direction or changing the deflection of backup rolls based on the calculated results of the element 6.