Disclosed is a technology relating to an agent system for generating an excellent plan. A script can be freely described by individually storing an action definition and the script without any limitation due to a language form of the action definition. Constructing as one of agent functions an update of knowledge using information acquired by execution, removes the necessity for the description of operations relating to an update in the plan. Diversification of contents of a replanning enhances a flexibility of the operations by an agent. Furthermore, when the agent moves among nodes, both of the agent and the node decide reliabilities of nodes to and from which the agent moves, so that a safety of information processing is improved. By preserving information used for restoring the agent at the time of the move of the agent, the agent having interrupted its action due to trouble can resume the action.