PURPOSE: To improve buffer utilization efficiency by providing a cell control system for a storage area with a cell assignment control table which is fitted with a cell assigning means and a return cell control means.

CONSTITUTION: When a returned assigned cell is in a basic area 1, it is connected to the effective cell queue anchor 5d of the cell assignment control table 5 and the number 5e of effective cells is increased by one. When a cell in an extension area 2 is returned, it is connected to the assignment cell queue anchor 5b and the number 5c of effective cells is increased by one. When the number 5e of effective cells exceeds a specific value, effective cells in the basic area are used as assigned cells, so they are connected to the cell queue anchor 5b. Even when assigned cells are returned continuously, they are returned to the pool, and when all cells are returned, a extension area cell control table 4 is released. Cells in the basis area are connected to the effective cell queue anchor 5d and the number of effective cells is increased by one; when the number attains to a specific value, cells are connected similarly.