PURPOSE: To improve the transmission efficiency and to attain high speed versatile service by applying an asynchronous transfer mode cell to N buffer memories, writing a data in each memory sequentially in the unit of cells and reading the data at the speed of the synchronous transfer mode base.

CONSTITUTION: A pay load ATM cell is sequentially extracted from a frame of STM-4c bases by four systems, a data is sequentially written in FIFO memories 61-64 and read simultaneously and a VP preset switch 10 is used to latch a time series and to output it demultiplexedly. Thus, an ATM cell arranged discontinuously in a frame of the STM-4c base is demultiplexedly by each system and the transmission efficiency of a broad band integrated services digital network (B-ISDN) is improved and the high speed versatile service is implemented.