An antenna device corresponds to a plurality of radio communications systems and frequency bands, can simultaneously carry out a reception and a transmission of different radio communications systems, and is capable of using antenna diversity by a simple construction. An antenna device comprises a first antenna matching with first, second, and third frequency bands, a second antenna matching with the third frequency band, a diplexer and the like. For signals of the first frequency band, a high-frequency switch circuit connects a transmitter or a receiver to the diplexer by switching. For signals of the second frequency band, an additional high-frequency switch connects a receiver or a transmitter to the diplexer by switching. For signals of the third frequency band, the additional high-frequency switch circuit and a further additional high-frequency switch circuit connect the second antenna or diplexer to a transmitter/receiver by switching.