The authors and their colleagues had developed a critical reading support software called “eJournalPlus,” which was designed to help learners not only read an electronic text but also construct their own opinions based on it. To create a rich learning environment that enhances critical reading when learners read electronic texts, we designed and implemented a collaborative learning function. The function was designed in the form of “push-pin comments,” which allows learners to directly exchange comments with each other on specific parts of a graphic organizer called “knowledge map” and on an essay generated by each learner through their individual reading processes. In this study, we examined the effects of this function on peer response activity that had the aim of improving the individual essays as products of their critical reading. The results showed that the push-pin interface facilitated learner peer response activities in which learners exchanged more critical comments on their peers’ knowledge maps and essays.