The aim of this study was to reduce the stress concentration of a medicine by dispersing the stress in tablets at tableting by addition of excipients. The mechanism of the stress dispersion was elucidated. Phenacetin (PHE) was used as a model of crystalline medicine with a high brittleness, and the degree of stress dispersion was evaluated by the change in the exposed surface area of PHE. To learn the mechanical strength of tablets, the crushing strength and friability were measured, their internal structure was analyzed by the porosity and pore size distribution, and stress relaxation experiments were performed. The results were as follows. Calcium silicate (Florite RE, FLR) showed a high stress dispersion effect, adding a high formability and mechanical strength to tablets. It was thought that the high stress dispersion resulted from the rapid stress relaxation caused by the plastic deformation and brittleness fracture of pores in FLR under a low compression pressure. Thus the stress caused locally on PHE particles may disperse.