The extension unit 3 includes a CPU 30 for performing calculation of various kinds of data and generation of control signals, a read-only ROM 31 in which data such as a start-up program and setting data 310 are stored, and a RAM 32 used as a temporal working area of the CPU 30.The setting data 310 shown in FIG. 3 is an expected value of a time (process time) from start of generation of one frame d