This study proposes a simple on-site estimation method of the floor stiffness. The contact stiffness depending on the preload between the support and floor is identified. The model of the preload-stiffness relationship for the block on the floor is described. The natural frequency of the block for the translational vertical vibration is measured by the impact test. The measurement is conducted for several blocks with different mass to obtain the preload-stiffness relationship. The contact stiffness coefficient is identified by fitting the model to the experimental data. The stiffness of two floors are compared using the estimation method to investigate the influence of its surface finish on the contact stiffness. The surface reinforcement using the glass coating increased the contact stiffness to 455% of that for the general polymer painted floor. The natural frequency of the block which has three supports is measured on the painted floor for verification of the identified parameter. The estimation using the identified contact stiffness coefficient well agrees to the experimental results.