A semiconductor integrated circuit device comprises a central processing unit (CPU), a first external terminal (EA0-EA16), and an electrically erasable and programmable nonvolatile flash memory (FMRY), wherein the semiconductor integrated circuit has a first operation mode in which the flash memory receives an address signal from the central processing unit executing a control program to erase and write data from and into the flash memory, and wherein the semiconductor integrated circuit has a second operation mode in which the flash memory receives an address signal on the external terminal to write data supplied from the outside of the semiconductor integrated circuit device into the flash memory.