A game software service system is connected to a monitor to display an image for game. A CPU and a PPU which cooperates with the CPU are accommodated within a housing. A plurality of storage mediums which respectively store game programs are attached to the housing in an attachable/detachable manner. The respective storage mediums are commonly connected to an address bus and a data bus of the CPU and the PPU, and assigned with a common address space. A first controller is used for playing a game. Any one of the storage mediums is selected by operation of a second controller. When a menu showing a plurality of game names is displayed on the monitor, accesses from the CPU and the PPU to a selected storage medium are enabled in response to the operation of the second controller. The CPU and the PPU execute a program of the selected storage medium to display the image for game on the monitor. In that state, when the first controller is operated, displaying condition on the monitor screen is responsibly changed by the CPU and the PPU.