The present invention relates to a device (1) for measuring knee laxity, with or without using additional diagnostic means, for assessing knee instability due to rupture of any ligament, i.e. the anterior cruciate ligament, posterior cruciate ligament, the posterior intracapsular and extracapsular ligaments, around the axes of an orthonormal referential that comprises three parts for receiving and immobilising the thigh, leg and foot respectively. The device (1) comprises independent means (20) and (21) for pushing backwards the anterior zone of the leg and for pushing forwards the posterior zone of the leg, and independent means (12) and (13) for pushing the posterior foot-supporting and -immobilising part (5) in the clockwise and anti-clockwise directions.
