To improve efficiency and reduce boot time by prefetching data by a cache system in units of a functional group.

In a boot system for a processor, a processor 101 starts desired processing by causing a DMA device 109 to read data from an external memory 113 into an internal memory 105 connected to the processor 101 without interposing the processor 101 at start-up or on changing a processing content. The boot system includes: a data dividing and storing means for storing the data; and a conversion table means for reading data from the external memory 113 into the internal memory 105 through the use of a conversion table 107 in which relation between the address of a block of data in the required external memory 113 and the address of the stored internal memory 105 is described.