An index calculator calculates, for a terminal device, an easiness-of-communication index indicating a degree to which a user using the terminal device recognizes communication, by using information related to the terminal device. A communication circuit receives communication request data of a first communication mode or a second communication mode from a first terminal device originating a call, the communication request data designating a second terminal device as a destination of the call. The communication circuit transmits, when the communication request data of the second communication mode is received and the easiness-of-communication index of the second terminal device meets a predetermined condition, communication request data of the first communication mode to the second terminal device.