Estimation of directional frequency transfer functions of floating offshore structures is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves). Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed. In two previous reports, the authors showed the inverse estimation of directional transfer functions of a floating offshore structure only using results of a few experiments in directional spectrum waves in a long towing tank. The response functions of wave exciting forces are treated in this paper. The precisions of estimated directional frequency response functions are confirmed using theoretical data.