A method of downloading a main code to a flash memory is provided. The method includes: comparing the size of the buffer with the size of the flash memory and determining a number of stages or segments in which the main code is to be downloaded to the flash memory based on the comparison results; obtaining a plurality of sub-main codes by dividing the main code by the determined number; generating a plurality of flash loader codes corresponding to the sub-main codes; and downloading the sub-main codes to the flash memory using the flash loader codes. Accordingly, it is possible to use the entire storage capacity of the flash memory even when the flash memory size is not smaller than the buffer size.