In this paper, we discuss the difference between expressed WTP for donation and actual donation for conservation of water wheels by considering hypothetical bias, which is certainty of payment action and recognition ratio of donation boxes. Especially we use the recognition ratio of people who found the donation boxes in the farmers' market near the water wheels. We found that the estimated WTP was 67.3 times higher than actual donation if we considered neither hypothetical bias nor recognition ratio. Next the difference was 48.7 times higher when we considered the bias of certainty only. Finally the difference was reduced to 1.57 times after we considered both hypothetical bias and recognition ratio.
