As a means to determine accurate boundary conditions, experimental identification techniques attract interest of engineers and many techniques have been proposed. In previous papers, the authors have proposed techniques to determine nonlinear boundary conditions with dynamical response and excitation data. But in practice, there are cases in which it is difficult to measure excitation data. Therefore, this study aims to propose a technique which does not require excitation data. Similarly to the previous techniques, it is imposed on the new technique to require neither the measurement nor the application of excitation at the boundaries. As a basic study for the technique, a beam is considered. In the proposed technique, the boundaries are modeled by springs and dampers as well as equivalent mass and moment of inertia, and their characteristics are determined by the harmonic balance method. Experiments are conducted, and the applicability of the proposed technique is confirmed.