To provide a robot which autonomously forms and performs an action plan in response to external factors without direct command input from an operator.When reading a story printed in a book or other print media or recorded in recording media or when reading a story downloaded through a network, the robot does not simply read every single word as it is written. Instead, the robot uses external factors, such as a change of time, a change of season, or a change in a user's mood, and dynamically alters the story as long as the changed contents are substantially the same as the original contents. As a result, the robot can read aloud the story whose contents would differ every time the story is read.