A flow control method includes a step of receiving individual data of each session from a network in an individual trunk apparatus and transmitting the received individual data as a transmission side common channel data to a common buffer, a step of temporarily storing data of plural sessions received from the individual trunk apparatus all at once and monitoring the congestion of the common channel according to the common buffer use amount, and upon detection of a congestion level, a step of stopping or limiting transmission of individual data of a session corresponding to a QoS class having a low priority from the individual trunk apparatus to the common buffer.