Dolphins detect, pursuit, and prey fish as their food by using their excellent sonar ability. If some advantages of their sonar such as object identification ability are introduced to our fisheries echo sounder, improvement should be possible because the purposes are similar. We focus on the wideband characteristics of dolphin's sonar in this study. We measured the frequency characteristics of the scattering amplitude of metal spheres and goldfish using the dolphin's sonar signal. We measured the absolute scattering amplitude of the metal spheres by the incident wave and the reflected wave by using sonar signals of bottlenose dolphin and finless porpoise. The measured scattering amplitudes agreed fairly well with the theoretical values in wideband. The scattering amplitudes of goldfish obtained in wideband were almost reasonable. These observations suggested that the dolphin possibly use the wideband scattering amplitude, which exhibits features of objects clearer than the echo spectrum, for the object identification.