For the purpose of predicting strongly nonlinear hydrodynamic phenomena, a CIP-based Cartesian grid method has been developed and validated through a comparison with measured time series of the local pressure induced by the green-water impact and observed flows around the ship's bow. However, hydrodynamic forces such as the added-mass and damping coefficients in the radiation problem have not been validated. Recently we carried out the forced oscillation tests in heave and pitch using a newly-constructed apparatus, which provided reliable data on the radiation forces. Thus a comparison is made between these data and numerically computed results by means of a CIP-based Cartesian grid method, the results are analyzed and discussed. And the accuracy of numerical result, and further development to be done are discussed at the end of the paper.