A method of the present invention includes: inputting a state transition diagram that represents first transitions between a plurality of states; inputting a mapping function that maps a given state to a value within a certain range; mapping each of the states with the mapping function to obtain mapping values, and perform grouping of the states into a plurality of groups based on the mapping values; for each of pairs of two groups obtained by combining two of the groups, setting a second transition from one group of the two groups to the other group when there is at least one first transition between therein; generating a representative transition path which is a sequence of the second transitions by tracing sequentially the second transitions; converting the representative transition path to a transition path in the state transition diagram; outputting the transition path as the test case.