A login management portion performs user authentication on the basis of a user ID and allows login of a user. A transfer control portion transmits, to a predetermined call transfer control device, a transfer setting request for causing a voice communication device to change an incoming call destination of a telephone number that corresponds to the user ID of the user whose login has been allowed. The login management portion prohibits, when a first user logs in, login of a second user different from the first user, and allows, when the voice communication device starts voice communication of the telephone number that corresponds to the user ID of the first user, login of the second user while prohibiting use of the voice communication device by the second user different from the first user.