In Part 2 of this paper the following pile driving formula has been found to have the bert applicabiliify to the case of steel pile: [numerical formula] where R_a: allowable bearing capacity (t) S: penetration of pile (cm) K: rebound (cm) e_f: efficiency F: driving energy of hammer (t・cm) Furthermore, the following formula has been derived from impact wave equation for the use of computing the impact stress at a pile head induced by the blow of driving hammer: [numerical formula] where σ_p: impact stress (t/cm^2) A_H, A_C, A_P: cross sectional area of hammer, cushion and pile, respectively (cm^2) H: height of drop of hammer (cm) α=0.141 for drop hammer α=0.324 for Diesel hammer.