In this research, at first, Bow-Diving phenomena of planing craft is measured in model test and the relative position between the hull and water surface at the time of Bow-Diving phenomena occurrence is investigated. The results show that the hull, which dropped the bow by a certain disturbance, begins to sink and Bow-Diving phenomena occurs. Next, the steady hydrodynamic forces due to the displacements of ship motions are measured, and the characteristics of the forces are investigated. Consequently, it became clear that the hydrodynamic forces, which return to the steady running attitude, do not act on the hull that dropped the bow greatly by a certain disturbance. Furthermore, the simplified estimation method that Bow-Diving phenomena occurs based on the forces is proposed.