Microfluidic devices using droplets make it possible to perform high-throughput screening of single-cell samples through encapsulating cells into droplets. In conventional encapsulation methods, devices have T-junction and flow-focusing geometry for droplet generation. Using those techniques, it is difficult to achieve uniform distribution of cells, or to place single cells in droplets. Moreover, in screening samples, it is necessary to have a mechanism to hold the droplets at one place for a long time. However, it is somewhat difficult to add such a function to conventional devices. Thus, we propose a new single-cell encapsulation method using triangular microwells. In this approach, each single cell is isolated, encapsulated, and held in one place by triangular microwells. This approach has the benefit that the droplet size can be regulated by the size of the microwells. In addition, optimization of encapsulation is easier than in conventional methods because the flow rate of the oil phase does not affect the encapsulation.