To provide a storage device-diagnostic device which diagnoses only an used area of a storage device to reduce diagnosing time required for diagnosing a storage device and executes efficient diagnosing processing, and also provide a diagnostic method therefor.

The information of a program A header 210 is first read, and it is recognized, from the number 214 of control programs, that there are three programs on a ROM, and the existence of three control programs on the ROM is confirmed from the presence-or-absence information on the respective three programs. Stored positions are recognized from the head address information of the respective control programs, and the whole control program is recognized from the head addresses and data sizes given to the headers of the respective control programs. Prescribed computation processing is applied to the control programs to compute computation processing result values, and whether the computed processing result values are in agreement with sum values 223. When these values agree, the control programs are determined to be normal, and, when these values do not agree, the data are determined to be broken.