Abstract: The present invention relates to a device (1) for measuring the knee laxity, with or without use of additional means of diagnosis such as computed axial tomography and magnetic resonance imaging, evaluating the instability of the knee due to rupture of any ligament, namely the anterior cruciate ligament, posterior cruciate ligament, postero-internal capsule, postero-external capsule, as well as around the axis of an orthonormal referential, that comprises three parts respectively to accept and retain the thigh, leg and foot. The device (1) includes independent means (20) and (21) to push backward the anterior zone of the leg and to push forward the posterior zone of the leg, and independent means (12) and (13) to push the part (5) for support and fixation of the foot in clockwise direction and in anti-clockwise direction.