PURPOSE: To prevent an accident in a railroad crossing by providing an existence detector in the railroad crossing, and feeding an alarm signal from a transmitter, receiving it by a receiver to report an alarm in the case that an output of detecting an obstacle is continued for a predetermined time or more.

CONSTITUTION: When an automobile C comes to a standstill by any trouble in a railroad crossing A, an existence detector 1 of using an ultrasonic wave, infrared ray, etc., is placed in a no-voltage output contact off-condition, and when this no-voltage output contact is continued off for a predetermined time, for instance, 30sec or more, the first alarm signal is fed by a transmitter 2, to turn on a light of an alarm device 3 by the first receiver 11 of receiving this alarm signal. This alarm report is seen to urgently stop an electric car by applying its brake by a motorman of the electric car advancing toward the railroad crossing A. Further in the case that the no-voltage output contact is turned off for 5min or more, the second alarm signal is generated from the transmitter 2, and by receiving this signal by the second receiver 5 in the nearest station, the obstacle C is informed of its existence in the railroad crossing A to a station employee.