© 2017 Elsevier B.V. Requirements for pellet injection system for a Japanese DEMO concept are comprehensively assessed in order to elucidate direction and target of R&D. A fusion output control simulation study using 1.5D transport code is carried out to estimate requirement of fuel particle source. Next, multivariable parameter dependence survey of the fuel deposition source on pellet speed, poloidal injection angle, pellet mass and pedestal height is performed. The conditions to achieve the target fueling depth derived from the output control study are shown. The AUG calibrated relation is referred to consider spatial restriction of tokamak geometry which relates maximum pellet velocity to curvature of pellet guide tube. Then the restriction is collated to the results of multivariable survey to find the most advantageous pellet speed, injection angle, and pellet mass which is consistent with both output control and tokamak geometry. Consequently, a conceptual design of fuel pellet injection system as the R&D target toward to DEMO is proposed.