A cardan shaft for a tool connected to a motor and provided with a system for checking conditions of use thereof. The cardan shaft has a rotatable shaft, with one or two end cardan joints. One or more sensor members are mounted on the cardan shaft to transmit signals to a data acquisition and data-processing electronic control unit (ECU) mounted on a fixed protection of the cardan shaft. The sensor members measure data such as torque transmitted by the cardan shaft, rotation speed of the rotatable shaft, vibrations of the cardan shaft, temperature of the cardan joint and articulation angle. A system for checking conditions of use of the cardan shaft has a remote node connected to the ECU and mounted on the fixed protection. The remote node acquires, stores and processes data sent to the ECU by the sensor members.