This study proposes a mobile support system “Stamp-On” to promote elementary school children’ scientific inquiry into museum exhibits. The unique characteristic of Stamp-On is its use of a stamp-shaped interface to connect exhibits and mobile device content in an extremely simple way. In this paper, we first describe the principles and implementation of the Stamp-On system. Then, we evaluate the performance of the Stamp-On system at a various rock exhibitions. For the evaluation, 35 Japanese sixth-grade elementary school children (aged 11-12) used the Stamp-On system. We recorded the actions and utterances of one of them during their scientific inquiry process. To clarify the effectiveness of Stamp-On, we have analysed the following two factors in the scientific inquiry processes: 1) observing subjects attentively and 2) interpreting information obtained through the observation. Based on these analyses, we conclude that Stamp-On is effective to promote scientific inquiry among children.