In order to have an antenna apparatus small in size and capable of switching its directivity pattern to be adaptive to multiple frequencies, the present invention provides an antenna apparatus having a first antenna element formed at an approximately center position of a planar printed circuit board and second antenna elements formed before and behind the first antenna element. It is possible to construct an antenna in which the first antenna element functions as a radiator and the second antenna elements function as a director or a reflector, respectively, by changing electrical length of the second antenna elements. The antenna becomes adaptive to multiple frequencies by feeding the second antenna elements at different phases to have the second antenna elements functioning as radiators.