An apparatus and a method for upgrading a program that controls a microprocessor. The program upgrading method includes: installing a Personal Computer Memory Card International Association (PCMCIA) interface device in the system; recording the upgrading program in a PCMCIA card; downloading the upgrading program from the PCMCIA card through the PCMCIA interface device installed in the system under the control of the program stored in the memory; and upgrading the program stored in the memory with the downloaded program under the control of the program stored in the memory. The program upgrading method can perform program upgrading through a PCMCIA interface easily.