PURPOSE: To save a required buffer quantity and to reduce frame split composition processing time by providing a means storing an intermediate result at transmission error control code generation and calculation and an intermediate result at error check and calculation using a transmission error control code in the unit of logic communication lines.

CONSTITUTION: In order to generate and calculate a transmission error control code while transferring transfer information with separation, an equipment 33 stores an intermediate result of transmission error control code generation and calculation for each logic line number. A cell 38 reached to a frame composition equipment 31 is shared by a cell share section 43, and an equipment 34 storing error check calculation and intermediate result using a transmission error control code applies error check calculation using a transmission error control code corresponding to a logic line number, deletes cell control information 39 and stores the result to a logic line buffer corresponding to an information storage buffer section 35. Since the error check calculation is implemented while composing a frame in this case, the equipment 34 stores the intermediate result of error check calculation for each logic line.