Previous studies (Frank, 1988; Toda, 1992) have shown the sense of unfairness to be an adaptive module within social environments. While adaptive modules can function effectively in practical contexts, they can be obstacles to solving insight problems (Knoblich, 1999; Hiraki & Suzuki, 1998; Abe & Nakagawa, 2007).   The purpose of this study is to test the effects of the sense of unfairness on problem solving. We hypothesize that the sense of unfairness will make it difficult to find the correct answer for this problem.To that aim, the ‘Transportation expenses problem’ is employed, which is a kind of insight problem with a social context.   In order to investigate our hypothesis, we asked participants to solve the problem. The results indicated that the participants did not make a correct and unfair response but a fair and incorrect one. Furthermore, we compare solution rates for the standard ‘Transportation expenses problem’ problem with isomorphic problems that do not involve need to think about unfairness. The results indicate that the solution rates for the isomorphic problems were higher than for the standard version of the problem. The results are supportive of our hypothesis.   The results of experiments suggest that the sense of unfairness interferes with the problem solving.In particular, it changes weight of each choice participants can select.