PURPOSE: To freely enable changing a function and performing the high-speed operation of a co-processor which assists the function of the processor and to provide the co-processor with functions required at every program in an information processor.

CONSTITUTION: The co-processor 12 consists of a large-scale PLD(Programable Logic Device) 12 whose functions can be freely changed by writing configuration data from an outside. An executive program is provided with configuration data, a writing means for configuration data, a configuration data write completion informing means and a co-processor starting means. Since the large scale PLD12 is provided with a rewritable memory and a logic part capable of changing operation according to the data recorded in the memory, the configuration data can be written into the memory of large-scale PLD12 at every executing program.