A vehicle speed regulating device holds the speed at a given value. It has an amplifier (1) fed by the vehicle battery (2). This receives a first signal given by a tachometer generator (3) driven from the vehicle wheels. It has a second signal from an adjustable rheostat (4) set to the desired speed. According to vehicle speed compared with set speed the amplifier delivers current either by a wire (5) of a wire (6) to drive an electric motor (7) one way or the other. The motor drives a mechanical regulator (8) to a stop (9), limiting the opening of the carburettor butterfly valve (10), also controlled by the accelerator pedal (11).