We have conducted hydraulic experiments in an open channel with cubic and rectangular shaped solid blocks on the slope for investigating the boulder transport process by tsunami. In our experiments, the block was mainly seen to be transported by a bore due to rolling or saltation rather than by sliding. Previous models for the boulder transport by tsunamis assumed sliding as a mode of transport for the boulder. Therefore, these models underestimated the distance of the boulder moved by the tsunami when it was transported due to rolling or saltation. In this study, we have developed a practical model for the transport of a boulder by tsunami, which takes into account the various transport modes. We introduce an empirical variable coefficient of friction by assuming that the coefficient decreases with decrease in ground contact time when the block was transported by rolling or saltation. With the aid of this parameter, the model can explain various modes of transport, i.e., sliding, rolling, and saltation, and reproduces the experimental results well. We further applied this improved model to a tsunami boulder at Inoda area in Ishigaki Island, Japan, which was transported by the 1771 Meiwa tsunami. The calculated distance of transport of the boulder was approximately 650 m, which is consistent with the description in the historical document. Based on our calculations, we estimated hydraulic values of the tsunamis. Estimation of such hydraulic values is important for understanding the behavior and power of the historical tsunamis, besides aiding future disaster mitigation efforts.