In a robot apparatus and a control method therefor, firstly, partial or whole state space of a behavioral model is expanded or reduced, secondly, transition to a predetermined node in the behavioral model is described as transition to a virtual node and a node group to be allotted to the virtual node is sequentially changed, thirdly, the number of emotions and/or desires which are used for generating actions is gradually increased, and fourthly, an environment is evaluated to update each sensitivity corresponding to each emotion and desire, on the basis of the evaluated. In the robot apparatus and the character discriminating method for the robot apparatus, a pet robot is provided with: detecting means for detecting outputs from other pet robots; character discriminating means for discriminating characters of the pet robots on the basis of the result detected by the detecting means; and character changing means for changing the character on the basis of the result judged by the character discriminating means.