As one of the beneficial resources reclaimable from municipal solid waste incineration residues (MSWIR), we studied the resource of cement and a dechlorination system to meet the JIS standard governing chlorine content in cement. A key problem of such a system is how to remove chlorines, especially insoluble chlorines such as Friedel's salt, from MSWIR by means of a low-cost treatment system. To develop an innovative dechlorination system for MSWIR, a pilot plant experiment to confirm the effectiveness of organic materials as additives for the dechlorination of MSWIR was conducted using large lysimeters. In addition, to estimate the chlorine-removal efficiency and the period required for sufficient dechlorination, a numerical simulation was carried out. In cases where no organic materials had been added to MSWIR, soluble forms of chlorine could be removed, but insoluble forms of chlorine - such as Friedel's salt, remained after treatment. On the other hand, when garbage compost was present as an organic additive, both soluble and insoluble forms of chlorine could be effectively removed. The removal of insoluble forms of chlorine was made possible by the decomposition of the insoluble forms resulting from a lowering of the pH level as a result of the decomposition of organic substances, and the generation of sulfuric acid derived from the decomposition of garbage compost. As a result, the total chlorine content of MSWIR can be decreased to 0.1% in about two years.