Abstract: Device for detecting the direction and change of rotational speed of a rotating element. In one embodiment, a pair of phototransistors which are energized by a light source according to an ordered sequence through a disk formed by opaque and transparent sectors coupled to the rotating element. The two phototransistors controls, when energized the switching on of two transistors which enable the discharge of two capacitors, charging with a predetermined time constant in the interval time between discharges. The discharge control action of one of the two phototransistors on a first capacitance is however conditioned by the charge level reached by the other capacitance and therefore both by the order in which phototransistors are energized and by the energization frequency. If the energization frequency is lower than a certain limit or the energization order is not the correct one, the first capacitor reaches a charge level higher than a reference value and supplies an indication signal accordingly.