A device (1) for carrying out measurements on a thin flexible tape material (6) comprises at least one pair of mutually spaced guide elements (23; 26; 27; 28; 29) which, on adjacent sides, are provided with identical curved guide surfaces (7, 8) which extend substantially parallel to each other, between which surfaces a guide channel (9) for the tape material is formed. In the guide surfaces supply ducts (17) terminate for supplying a pressurized gaseous medium to both sides of a tape material in the guide channel. In the longitudinal direction the tape material can be guided in the guide channel by means of the medium along a curved path which is substantially parallel to and spaced from the guide surfaces. In each of the guide surfaces a termination (22) of at least one measuring duct (21) is situated, the terminations being arranged at least substantially directly opposite each other, in a pair or pairs which measuring ducts communicates with at least one pressure transducer (19) which is connected to measuring means (25). By determining the pressure difference on each side of the tape material with the aid of the measuring means the device enables local tensile stresses in the tape material to be measured.