Tensile testing machine, said machine comprising: - a frame provided with a first fastening element at a first end of a test specimen whose elongation is to be measured along a tensile axis, - tensile means adapted to exert a traction along the tensile axis and provided with a second fastening element, forming an axial bar, at a second end of the specimen, coaxially to the tensile axis, - a first sliding plate slidably mounted along the second fastening element and on which a first part of elongation measuring means for measurements of said elongation parallel to the tensile axis is mounted, - a second intermediate plate, which is fixed to the second fastening element and to which a first guide rod is fixed, the first guide rod extending parallel to the tensile axis and passing freely through the first sliding plate, - a third sliding plate, which is slidably mounted along the second fastening element and to which a second part of the elongation measuring means is fixed, - first and second deflection rods (52, 54), adapted to sense the first and second fastening elements (22, 24), respectively, the second deflection rod passing through the first sliding plate and coming to bear against the third sliding plate, to act on it parallel to the tensile axis, so that the elongation measuring means can detect, parallel to said axis, a displacement between the first and third sliding plates (44, 50), the tensile testing machine characterised in that: - the tensile testing machine further comprises -- an elastic return means returning the first and third sliding plates (44, 50) towards each other axially, -- a second guide rod parallel to the first guide rod, which freely guides the first and third sliding plates (44, 50) axially, by being disposed at their level, and - the first deflection rod is fixed with the first sliding plate through which the second deflection rod passes. - a frame provided with a first fastening element at a first end of a test specimen whose elongation is to be measured along a tensile axis, - tensile means adapted to exert a traction along the tensile axis and provided with a second fastening element, forming an axial bar, at a second end of the specimen, coaxially to the tensile axis, - a first sliding plate slidably mounted along the second fastening element and on which a first part of elongation measuring means for measurements of said elongation parallel to the tensile axis is mounted, - a second intermediate plate, which is fixed to the second fastening element and to which a first guide rod is fixed, the first guide rod extending parallel to the tensile axis and passing freely through the first sliding plate, - a third sliding plate, which is slidably mounted along the second fastening element and to which a second part of the elongation measuring means is fixed, - first and second deflection rods (52, 54), adapted to sense the first and second fastening elements (22, 24), respectively, the second deflection rod passing through the first sliding plate and coming to bear against the third sliding plate, to act on it parallel to the tensile axis, so that the elongation measuring means can detect, parallel to said axis, a displacement between the first and third sliding plates (44, 50), - the tensile testing machine further comprises -- an elastic return means returning the first and third sliding plates (44, 50) towards each other axially, -- a second guide rod parallel to the first guide rod, which freely guides the first and third sliding plates (44, 50) axially, by being disposed at their level, and -- an elastic return means returning the first and third sliding plates (44, 50) towards each other axially, -- a second guide rod parallel to the first guide rod, which freely guides the first and third sliding plates (44, 50) axially, by being disposed at their level, and - the first deflection rod is fixed with the first sliding plate through which the second deflection rod passes.