PURPOSE: To attain automation of normal supervision of a level of a communication device and a transmission line by providing a means for measuring a transmission/ reception signal level and a means for transmitting automatically the measured level.

CONSTITUTION: A level processing section consists of a level measuring command section 41, a level measuring section 42 and a level data transmission processing section 43, a signal transmitted from a data processing unit 1 is received via a reception section R and when the command is addressed to the own station, the transmission command of the level data is given to the level measuring section 42 and the level data transmission processing section 43. The level measuring section 42 receiving the command measures the level of the communication device and transmission line and its measured data is inputted to a transmission section T together with the own station identification code from the level data transmission processing section 43 and transmitted from the transmission section T. When the measured data of other station is received, the received data is given as it is to the level data transmission processing section 43 and transmitted from the section T. Thus, the level of many communication devices and transmission lines is grasped at any time by a master station and unattended supervision for the propriety is attained.