  To realize autonomous collaborative robots, it is important to increase the
trust that users have in them. Toward this goal, this paper proposes an
algorithm which endows an autonomous agent with the ability to explain the
transition from the current state to the target state in a Markov decision
process (MDP). According to cognitive science, to generate an explanation that
is acceptable to humans, it is important to present the minimum information
necessary to sufficiently understand an event. To meet this requirement, this
study proposes a framework for identifying important elements in the
decision-making process using a prediction model for the world and generating
explanations based on these elements. To verify the ability of the proposed
method to generate explanations, we conducted an experiment using a grid
environment. It was inferred from the result of a simulation experiment that
the explanation generated using the proposed method was composed of the minimum
elements important for understanding the transition from the current state to
the target state. Furthermore, subject experiments showed that the generated
explanation was a good summary of the process of state transition, and that a
high evaluation was obtained for the explanation of the reason for an action.
