PURPOSE: To improve the processing performance of a communication controller by decomposing communication data on a basis of decomposition table data having a prescribed logic and directly storing data in a data buffer and a control buffer.

CONSTITUTION: Communication data is inputted from a communication destination 1 to a decomposing device 2 through a communication medium 6, and the device 2 decomposes communication data on a basis of a decomposition table 3. A control signal is inputted from the device 2 to a communication controller 4 to start the controller 4. The controller 4 discriminates whether program data stored in a data buffer 8 is correctly received from the communication destination 1 or not on a basis of control data stored in a control buffer 2. If it is correctly received, a control signal is inputted to a program 5 from the controller 4 to start the program 5; but if it is not correctly received, program data is abandoned. Data stored in the buffer 8 is referred to perform the processing by the program 5.