A control apparatus controls an agent apparatus functioning as a user interface of a request processing apparatus that acquires a request indicated by at least one of a voice and a gesture of a user and performs a process corresponding to the request. The control apparatus includes a transmission event detecting section that detects an occurrence of an event necessitating transmission of a message to a communication terminal of the user, and a transmission determining section that makes a determination to transmit a voice message to the communication terminal of the user, via a communication network, if an occurrence of the event is detected.