C10-PbI4, a layered perovskite-type material, has been studied with emphasis on its linear and nonlinear optical properties. It has been found that this material is a natural quantum-well system, in which excitons are confined in a thin inorganic layer sandwiched between organic barrier layers. Very clear two-dimensional characters of the lowest exciton, its large binding energy and large third-order optical nonlinearity have been found.