Wave forces and wave pressure acting on an axisymmetric caisson with slanting upper wall were investigated through hydraulic experiments and theoretical analyses. The vertical distributions of horizontal wave force were well estimated by the Morison's formula with velocity distribution calculated by the nonlinear wave theory and variable inertial force coefficient calculated by the diffraction wave theory. The horizontal wave force calculated by the linear diffraction wave theory is larger than the experiment results. The theory to evaluate the vertical wave force acting on the bottom of the caisson was developed based on the 2-dimensional infiltration equation. The vertical wave force is found out to change according to the water permeability of the sea bottom.