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.