In previous studies, dam-break tests and computational fluid dynamics have conducted to clarify the characteristics of tsunami loads acting on the building structure with upstream obstruction. However, the Froude number in the dam-break tests are changed from time to time. It is found that the drag force acting on a structure in subcritical flow is affected by the Froude number. For simplicity, this study focuses on the drag force on building structure with upstream obstruction in subcritical flow where the Froude number is uniform.