研究成果概要：The supplier network of a firm is now increasingly viewed as an important source of innovation in new product devel...The supplier network of a firm is now increasingly viewed as an important source of innovation in new product development. The “hub firm” role of a manufacturer enables it to set up its supplier network. They sometimes expect suppliers to cooperate with each other while maintaining the suppliers’ competition. The study investigated the influences of horizontal supplier–supplier competition and cooperation in the supplier network on the innovation of the ego buyer from the view of an ego network. It takes the supplier network of an ego buyer as an analysis unit, using cross-sectional data of 130 listed Japanese buyers in manufacturing industries and their first-tier supplier networks in 2016. The results indicate that both supplier–supplier competition and cooperation have inverted U-shaped effects on buyer innovation. It contributes to recent research on networked supply relations through a new attempt to link traditional horizontal coopetition among suppliers with the innovation of the vertical buyer. It also provides manufacturers insights on how to strategically manage horizontal supplier–supplier relations for its product innovation.