This paper proposes a new diffusion coefficient which considers the variation of chloride binding and evaporable water in concrete. A FEM (Finite Element Method) program developed on the basis of the new diffusion coefficient provides an estimation of chloride concentration with concrete depth and aging, and predicted chloride concentrations are compared with experimental values.The apparent diffusion coefficient, which is presented as functions of chloride binding, evaporable water and intrinsic diffusion coefficient, varies greatly according to water-cement ratio. But, curing temperature does not have a significant influence on the ratio of apparent diffusion coefficient to intrinsic diffusion coefficient. The FEM program using the apparent diffusion coefficient estimates experimental chloride concentrations in a little error range. On the contrary, chloride penetration analysis using intrinsic diffusion coefficient overestimates the penetration depth of chloride ion. Therefore, it is recommended to use the apparent diffusion coefficient for predicting the initiation age of chloride-induced corrosion