This paper describes a group attention control (GAC) system that enables a communication robot to simultaneously interact with many people. GAC is based on controlling social situations and indicating explicit control to unify all purposes of attention. We implemented a semi-autonomous GAC system into a communication robot that guides visitors to exhibits in a science museum and engages in free-play interactions with them. The GAC system's effectiveness was demonstrated in a two-week experiment in the museum. We believe these results will allow us to develop interactive humanoid robots that can interact effectively with groups of people. Categories and Subject Descriptors H.5.2 [Information Interfaces and Presentation]: User Interfaces