A main robot apparatus generates a sound scale command at a command generating state (ST2) to enter into a state of waiting for a reaction of a slave robot apparatus (ST3). When the slave robot apparatus outputs a emotion expressing sound responsive to a sound scale command issued by the main robot apparatus, the main robot apparatus recognizes this emotion expressing sound to output the same emotion expressing sound. In a state of the reaction action (ST4), the main robot apparatus selects an action (NumResponse), depending on the value of the variable NumResponse which has counted the number of times of the reactions to output the action.