PURPOSE: To automatically detect interrupt entry without allowance and make a display of intention to a succeeding vehicle.

CONSTITUTION: The CPU 11 of a control part 1 confirms the travel direction changing intention of a vehicle occupant by the on state of a direction indicator 2 and detects the travel direction of a vehicle by integrating the output signal of a yaw rate sensor 3. The CPU 11 also detects the inter-vehicle distance to a succeeding vehicle by an inter-vehicle distance sensor 4 and makes a display of intention to the succeeding vehicle by an emergency blink light 5 in the case of the inter-vehicle distance to the succeeding vehicle being the set value or less at the time of detecting that the vehicle being returned to the original direction after being changed.