This report describes an application of relaxation technique to the alternating direction implicit finite-difference time-domain (ADI-FDTD) method. The ADI-FDTD method is quite stable even when the CFL condition is not satisfied. However, the ADI-FDTD method is computationally more complicate than the conventional FDTD method and this method requires to solving the tri-diagonal matrix equation. Thus, this method may require more computational cost than the standard FDTD method due to the large scale tri-diagonal matrix solution corresponding to a large number of meshes. In this report, relaxation-based solution technique is discussed for the matrix solution and a simple numerical example is shown. As a result, it is confirmed that ADI-FDTD method with the relaxation technique is useful for the acceleration of the electromagnetic field simulation.