To certainly execute a rewriting program performing a process for rewriting firmware.

A system controller decides whether receiving a rewriting instruction of the firmware from a host PC in S1, reads the rewriting program stored in a program memory to move it to a buffer memory in S2 when receiving the rewriting instruction, executes the rewriting program on the buffer memory in S3, receives a program of a new master from the host PC to store it into the buffer memory in S4, erases a program area of a master of the program memory to erase the program of the master stored in the program memory in S5, reads the program of the new master stored in the buffer memory to write it into the program memory in S6, and writes a writing completion flag into the program memory in S7.