Periodic structure plays important role with its sensitivity for frequency in microwave communication and optical integrated circuit system [1][2]. Also, in optical fiber communication[3], such periodic structure is used for supporting optical wave to be guided in core of the fiber. In such application, a defect in the structure generally works as a cavity or a waveguide by making use of its high selectivity. However, by lacking periodicity in the structure with a defect, general mathematical approaches have often difficulties, due to inconvenience in description of the problem. In such cases, computational simulation technique for electromagnetic wave propagation and scattering is very important and effective. By the recent development of computers, it is possible to model a large scale periodic structure with defect.