To realize partial rewriting during operation by accessing a connection storing part, a cell enable storing buffer, etc., in response to an instruction from a CPU so as to control input/output to the individual cell of a logic cell and an I/O cell.

This system is provided with a connection storing part 8 which stores switching information for mutual connection between wirings within PLD and a logic cell 24, an I/O cell 27, and with a cell enable storing buffer 9 for storing data for controlling input/output to the individual cell of the cell 24 and the cell 27. In addition, the system is provided with a cell enable timing generation circuit 13 for generating a writing signal 12 for shifting the contents of the buffer 9 for batch-changing input/output control data of the cells 24 and 29 to a cell enable storing part 11. Input/output to the individual cell of the cells 24 and 27 is controlled by this constitution to eliminate the effect of a rewriting part on other circuits inside or outside of PLD when rewriting PLD.