The cell-immobilization technique is used for the physical and chemical fixation of cells onto a solid support in order to increase their stability and capacity of substrate uptake. However, there is no apparatus to observe the microbial community's structure inside cell immobilizing polymeric carrier. In order to satisfy the demand of monitoring for the microbial distribution inside the carrier, we developed an automatic phase contrast microscopic monitoring system capable of determining the microbial density and distribution inside a cell-entrapped carrier automatically.