In this paper, we present a void topology identification analysis in structures based on the level-set-based topology optimization using a weighted sensitivity method. The void topologies are identified by using the observed hammering response data and the gradient of the Lagrange function with respect to the level-set function. The numerical simulation of structural oscillation is performed by the finite element method, and the void topology identification analysis is formulated by the adjoint variable method. An improvement of how to give numerical parameters in the weighted sensitivity method is conducted, and numerical tests are carried out for minimization problem of the Rosenbrock function. The improved procedure is applied for the void topology identification analysis, and applicability of the proposed method is shown in this paper.