To provide an optical disk recording/reproducing device capable of accelerating version-up processing by omitting erasing processing for erasing the contents of a flash memory to zero at the time of version-up grading.

When the power of a device power supply is turned on for example as preparation before performing version-up grading processing, a memory processing part 4 is started in the preparation processing. Thereby the final address of a firmware program in the flash memory 1 is set by a final address setting means 41, whether the set final address is the final address of the flash memory 1 or not is determined by an address determination means 42, and when a state that the final address is not the final address of the flash memory 1 is determined, contents from a succeeding address of the final address up to the final address are set to zero by a zero setting means 43, so that erasing processing for version-up grading can be omitted.