PURPOSE: To improve response to control and to prevent the occurrence of high hunting during limitation of a car speed, by a method wherein a real time is controlled as a car speed is checked each time a car speed detecting pulse is generated.

CONSTITUTION: When a car speed exceeds a limit speed, an overspeed detecting signal from an overspeed detecting circuit 5 is generated in synchronism with a car speed detecting pulse from a car speed detecting signal output circuit 4, and during the generation of overspeed detecting signal, charging of a capacitor C1 for holding of an ignition block signal output circuit 6 is blocked. Thereby, the terminal voltage of the capacitor C1 for holding can not exceeds a set value, and an ignition block signal is outputted. Since this state is continued as far as a car speed exceeds a limit speed, an ignition block circuit 7 stops the motion of an ignition device and forces an engine to fail in ignition to reduce a rotation speed. This constitution enables block of an ignition motion according to an overspeed detecting signal provided by performing integrating computation each time a car speed detecting pulse is generated.