This study was accomplished to develop a pneumatic granular applicator that can be attached to the conventional ride-on rice transplanter. Operating conditions of a metering device for the applicator were determined so as to obtain the required discharge rate of granules for field application. The shape and size of diffuser was selected for the applicator and the spacing between diffusers on a boom and the boom height were determined as an optimal application condition for uniform distribution. The diffuser spacing of 1m for the fertilizer and the diffuser spacing of 0.8m for the pesticide at the boom height over 0.8m were acceptable.