As shown in FIG. 3, client terminal device 1 comprises CPU 30, graphics processor 31, and IO processor (IOP) 32. [0059] In addition, client terminal device 1 comprises optical disk controller 33, which controls reproducing of an optical disk such as a CD-ROM or DVD-ROM, and sound processor unit (SPU) 34. [0060] In addition, client terminal device 1 comprises MASK-ROM 35, which is stored with an op