PURPOSE: To enable it to shorten an operation interval by measuring the distance of a preceding train from a receiving end of a block section, transmitting it to a signal processor installed at the side of this receiving end, and when the above distance is more than the specified value, controlling a signal so as to permit the admission of a succeeding train into the block section.

CONSTITUTION: When a preceding train (A) is entered into a block section 101, a drive relay 6 is dropped by the lowering of output in a receiver 4, and a red lamp of an intermediate signal 5 is lighted and any admission of a succeeding train (B) into the block section 101 is prohibited. On the other hand, at a car-mounted transmitter 10, a travel distance of the train secured by operation so far is cleared each time it enters a new block section, and a signal out of a tachometer generator 11 is transmitted to a relay 1 by an antenna 12. This signal is inputted into a signal processing circuit 22, calculating a proceeding position of the train from the receiving end is calculated, and when the value has come to the specified distance, a red lamp R and a yellow lamp Y of the intermediate signal 5 are lighted, thereby permitting the admission of the succeeding train (B) into the block section 101.