This paper reports how robot-assisted language learning (RALL) impacts Japanese adults' English speaking skills. With existing research on RALL focusing on children, there is little evidence indicating RALL's effects on adults. We developed a RALL system comprising a robot, a tablet, and designed learning materials for speaking practice. To explore the effects of this system on the speaking skills of adults, we conducted a pretest and posttest designed pilot experiment. The participants in this study were nine female Japanese university students. The participants used the system for speaking practice for a total of 30 min per day for 7 days. The results of comparing the pretests with the posttests demonstrated that the adults' English speaking skills were enhanced; in particular, their speaking accuracy, fluency, and pronunciation improved greatly. This study contributes to providing clear evidence of the effects of RALL on Japanese adults' English speaking skills.