Cell transfer rate control apparatus and method

A load observation unit (13) observes a load using each quality class buffer (14a) and the link (address management unit (14)) accommodating quality class buffers (14a). An ER computation unit (16a) computes an ER (explicit cell rate) for each quality class buffer (14a). The ER can also be computed by the entire link. The ER computation unit (16a) defines the ER computed for the quality class buffer (14a) or the ER computed for the entire link, whichever is larger, as a first ER. Then, it compares the first ER with the MCR (minimum cell rate) set in the connection of the quality class buffer (14a), and defines one of them whichever is larger as a second ER. Then, the value of the ER set in the ER field of the RM (resource management) cell arriving at the quality class buffer (14a) with the above described second ER, and the value whichever is smaller is set in the ER field of the RM cell.