A relay device that includes a telephone relay unit and a wireless communication relay unit, wherein the telephone relay unit receives call information from a telephone (20, 22) via a network, and after a communication partner designated by the call information has responded, transmits/receives a voice signal to/from the telephone (20,22), the wireless communication relay unit, to which a repeater (25, 27) that is a relaying radio is connected, transmits/receives a voice signal to/from a radio via the repeater (25, 27), the telephone relay unit determines a destination apparatus that is a radio to be called based on the call information received from the telephone (20, 22), and transfers a voice signal received from the telephone (20, 22) to the wireless communication relay unit, the wireless communication relay unit transfers a voice signal transferred from the telephone relay unit to the destination apparatus, the telephone relay unit includes: a call destination table in which a record including the call information, an address of the destination apparatus, and an apparatus type of the destination apparatus is stored for each of the radios; and a transfer control table in which a record including the apparatus type and a transfer control mode of a voice signal is stored for each of the apparatus types, and the telephone relay unit determines the apparatus type of the destination apparatus by referring to the call destination table, determines the transfer control mode of a voice signal corresponding to the determined apparatus type by referring to the transfer control table, and transfers a voice signal to the wireless communication relay unit using the determined mode. wherein the telephone relay unit receives call information from a telephone (20, 22) via a network, and after a communication partner designated by the call information has responded, transmits/receives a voice signal to/from the telephone (20,22), the wireless communication relay unit, to which a repeater (25, 27) that is a relaying radio is connected, transmits/receives a voice signal to/from a radio via the repeater (25, 27), the telephone relay unit determines a destination apparatus that is a radio to be called based on the call information received from the telephone (20, 22), and transfers a voice signal received from the telephone (20, 22) to the wireless communication relay unit, the wireless communication relay unit transfers a voice signal transferred from the telephone relay unit to the destination apparatus, the telephone relay unit includes: a call destination table in which a record including the call information, an address of the destination apparatus, and an apparatus type of the destination apparatus is stored for each of the radios; and a transfer control table in which a record including the apparatus type and a transfer control mode of a voice signal is stored for each of the apparatus types, and the telephone relay unit determines the apparatus type of the destination apparatus by referring to the call destination table, determines the transfer control mode of a voice signal corresponding to the determined apparatus type by referring to the transfer control table, and transfers a voice signal to the wireless communication relay unit using the determined mode. a call destination table in which a record including the call information, an address of the destination apparatus, and an apparatus type of the destination apparatus is stored for each of the radios; and a transfer control table in which a record including the apparatus type and a transfer control mode of a voice signal is stored for each of the apparatus types, and the telephone relay unit determines the apparatus type of the destination apparatus by referring to the call destination table, determines the transfer control mode of a voice signal corresponding to the determined apparatus type by referring to the transfer control table, and transfers a voice signal to the wireless communication relay unit using the determined mode.