A three-dimensional virtual space simulator comprises a section for determining the action of an avatar according to the input by the user and generating action instruction data representing the content of the action, a section for determining the action of an agent autonomously and generating action instruction data representing the content of the action, and a process control section for displaying each character in a virtual space according to the action instruction data received from the sections wherein the process control section and a graphic process section share an interface for receiving the action instruction data from the avatar action instruction section, and an interface for receiving the action instruction data from the agent action instruction section. Consequently, a flexible participation mode of the user and high reliability are realized.