Herein the possibility of the FDTD method, which considers longitudinal and shear waves and two types of damping terms, is investigated as a new prediction method for architectural structure-borne sound. Equations of motion and Hooke’s laws of three-dimensional elastic bodies are directly discretized with a difference scheme of the leap-flog algorithm. Using these formulations, vibration-mode transformations at the junctions of building frames can be considered without special handling. This method seems to be especially effective for providing both visible and audible predictions because time responses can be obtained directly. First, the formulations and the stability condition are discussed. Next, a parallel computing algorithm to efficiently perform the FDTD calculation is introduced. Finally, the predicted results are compared to the measured data from the viewpoints of energy decay and frequency characteristics. From these comparisons, it is confirmed that the predicted results and the measured data are in good agreement if the appropriate damping terms are employed.