Gamification, using game elements in nongame contexts, is widely recognized for its efficacy in training individuals within organizational and academic environments. Specifically, it has gained significant attention in training to operate complex systems like enterprise resource planning (ERP). However, research has generally overlooked how gamified training changes users' ability and motivation through eustress (challenging and positive stress). To address this gap, this study proposes that gamified training can increase users' ability and motivation. Self-efficacy and involvement are examined as representations of ability and motivation, respectively. Furthermore, we hypothesize that users' pre-training self-efficacy and involvement positively affect eustress experienced during gamified training, subsequently affecting post-training self-efficacy and involvement. To test research hypotheses, data were collected from 205 graduate students who participated in an ERP simulation game. The findings indicate a significant increase in self-efficacy and involvement after gamified training, substantiating the potential of gamification to enhance these aspects. Moreover, the study demonstrates that initial self-efficacy in learning ERP systems influences the experience of eustress during gamified training, ultimately impacting post-training self-efficacy and involvement. Our research sheds light on the transformative impact of gamified training and eustress in learning complex systems, providing valuable insights for gamification implementation in training practices.