PURPOSE: To enable a mobile radio system to select accurately channels within a narrow frequency band by detecting the coincidence between the specific code of a main station and that of a subordinate station.

CONSTITUTION: In the broadcast system consisting of main station 1 and subordinate stations 2 to (n) to which specific codes are assigned respectively, the main station sends a code signal equivalent to a subordinate station which the main station desires to select and the subordinate station, on the other hand, makes discrimination 15 whether or not the code signal through reception 11 agrees with with its own specific code, so that when they agree each other, code signal 16 which corresponds to the received code signal will be sent back to the main station. Receiving the return signal from the subordinate station, the main station confirm the channel-selected subrodinate station and then starts the fixed broadcast