This study aims to design a virtual world agent's behavior based on the cognitive architecture ACT-R that aims to simulates the human mind. At this time, the hierarchical architecture is implemented to combine modules of decision making and body movement by using ACT-R and a three-dimensional game engine respectively. Each module collaborates to work via the communication server, realizing independency between two modules. The goal of this study is to develop a method of designing various behaviors of agent based on the hot swapping the ACT-R model or the modulation of parameters of the model.