To provide an information processor capable of installing patch programs that are equal to or more than a prescribed amount and performing patch processing.

This processor is provided with a flash ROM 12 and a RAM 13, and is managed by a particular OS that can perform a patch program stored at a prescribed position on the RAM 13. By inserting a CF (compact flash) card 14, a patch installer 41 is applied to copy the patch program 42 into a patch area (second ROM image area) 22 of the flash ROM 12, and an additional patch file 43 obtained by filling a part of the patch program which exceeds the capacity of the patch area 22 is also stored in a disk area 23. Patch processing is performed in such a manner that the OS writes the patch file on the disk area 23 to a prescribed position of the RAM 13 after resetting.