A mobile terminal device having an antenna switch able to efficiently switch connection between reception signals from a plurality of antennas and signal processing circuits of the reception signals is provided. The device is able to communicate by a first data transmission system performing a diversity reception and a second data transmission system not performing the diversity reception. The device includes: a first antenna; a second antenna; an antenna attachable and detachable and detachable portion, to which a third antenna is attached and from which the third antenna is detached; a first wireless circuit for performing communication using the first antenna or the third antenna; a second wireless circuit for performing communication using the second antenna; a third wireless circuit for performing communication using the first antenna or the third antenna; and an antenna switch.