Method and apparatus for controlling communication band in data communication system

[Problem] Provided are a communication band control method and apparatus wherein a single error correction circuit is used to be able to support even a communication system in which the unevenness or variation of error rates is significant and to prevent inequity from occurring among users. [Solution] In a data communication system in which a first communication device (91) is connected to a plurality of second communication devices (93, 94) via communication paths (82), a communication band control apparatus determines an encoding rate of the communication between the first communication device and each of the plurality of second communication devices on the basis of the error rate estimated from that communication and controls the time allocations of a communication band to the respective communications on the basis of the encoding rates.