Whether people punish an unfair partner has been investigated using the ultimatum game, in which a proposer makes an offer of how to divide a fixed amount of money between him/herself and a responder, and the responder decides whether to accept or reject the proposer's offer. Previous studies have revealed that it is the proposer's unfair intention, rather than the unfair offer itself, that increases the rejection rate. However, all of the previous studies employed the strategy method, wherein the responders had to decide whether to reject various offers before examining the proposer's actual offer. The primary purpose of the present study was to examine whether the effect of unfair intention would be replicated when the responders made their decision upon receipt of the proposer's offer. Accordingly, in the present study, participants received an unfair offer (i.e., the proposer would take 90% of the resource) that was made intentionally or unintentionally, and then decided whether to accept it. The result showed that the unfair offer was rejected more frequently in the intention condition than the no-intention condition.
