A communication system has a personal computer (PC) which obtains a communication function by acquiring a modem driver, and a portable communication terminal which can communicate with the PC. The portable communication terminal includes a USB interface section to be connected to the PC, a RAM storing an address of a server that stores the modem driver, and a control section which downloads the modem driver from the server through a wireless communication section, and transmits the downloaded modem driver to the PC through the USB interface section.