In tsunami hazardous area, tsunami evacuation buildings are expected to save many people from tsunami. For tsunami evacuation buildings, enough capability against tsunami force should be considered. In Tohoku giant earthquake tsunami, many concrete buildings have been damaged and it is important to estimate the tsunami force on buildings. In this paper, the tsunami force on the buildings is investigated based on numerical simulation. In the simulation, the openings of the buildings, space in the buildings and structure types are considered. Simulation result reveals that the tsunami force decreases with increasing a size of openings. Moreover some mechanism of behavior of run-up tsunami passing through a piloti of the buildings is clarified.