Abstract: The sensor of the invention comprises a flexible beam of a rectangular cross section with rigid solid end blocks at both ends for securing the sensor in a tester. The beam has two symmetrically-shaped through slots cut in mutually perpendicular directiors so that they are partially intersect within a body of the beam. Each slot has at its opposite ends notches which are wider than the slots so that the distance from the inner wall of the notch to the outer side surface of the beam is shorter than the distance to this surface from the inner wall of the slot. Strain gauges are attached to mutually perpendicular surfaces at the ends of the beam which are flexible in the direction of the force being measured and are rigid in the perpendicular direction. Under effect of the loading force and of the friction force, the flexible beam acts as a pair of overlapped and mutually perpendicular parallelograms.