Diffuse reflection spectra are measured for (PbI2)5clusters incorporated into supercages of zeolite LTA crystals, where the Frenkel exciton of cluster crystal is expected to be realized. The reflectivity at the exciton resonance energy drastically increases as the loading density nears the saturation level. This result can not be interpreted by the increase of the cluster density, but by the cluster ordering. We propose the order-induced decrease in the damping energy of the Frenkel exciton, because the motional narrowing of the exciton is expected in the ordered (PbI2)5clusters. Electron diffraction pattern shows that clusters are arrayed in twice period of the zeolite cages.