Abstract: A safety and test device for railway signalling systems comprising a calculating device or computer adapted to treat information signals, relating to prevailing speed and desired speed, and to activate a brake device if said treatment reveals that speed reduction is necessary. In order to control itself the computer is programmed to run through special test programs, suitably sections of the ordinary program with given start data, and at the end of each such test program generate a control word, specific for each test program and coming in a given sequence. A control unit connected between the computer and the brake device receives the control words generated by the computer and compares them with correct words stored in a memory and generates an output pulse, each time an incoming control word coincides with a correct control word stored in the memory.