To reduce a cost by performing tuning work using an inexpensive arrangement without use of a microcomputer including a RAM dedicated to tuning and having a rewriting feature for the RAM.

A CPU decides based on I/O retention data whether external equipment is connected (step S1). If the external equipment is not connected (No at step S1), a base pointer is specified in a ROM (step S2). If the external equipment is connected (Yes at step S1), whether transfer of constant data from the ROM to a RAM is completed is decided (step S3). If No, data stored in a constant area in the ROM is transferred to the RAM (step S4), and the base pointer is specified in the ROM. In contrast, if step S3 results in Yes, the base pointer is changed to the RAM (step S6). The ROM and RAM are then accessed through relative addressing based on the base pointer (step S7).