PURPOSE: To evaluate how easily a system is used easily and objectively by deciding elements in a set of last inputs at the time of transition to respective states according to a state transition table.

CONSTITUTION: This device includes a state transition table storage means 101 stored with the state transition table, a state set generating means 102 which generates a set of all states appearing in the state transition table by referring to the state transition table storage means 101, and a last input set generating means 103 which generates a set of last inputs by states as elements of the set by referring to the state transition table storage means 101. Further, this constitution includes a constitency evaluating means 104 which evaluates the consistency of the last inputs by receiving the output and counts elements of the set of last inputs. Consequently, it is decided automatically whether or not the last inputs in respective states has consistency as to the system whose operation is described in the transition state table and when how easily the system is used is evaluated, a part originating from the consistency of the operation is decided automatically.