An antenna device comprising: an element part including an excitation element (1a,1b) having a feed point for a radio frequency signal; a first passive element (11a, 11b) disposed at a position apart from said excitation element (1a,1b) and having first conductive part and second conductive part; a second passive element (21a,21b) disposed at a position apart from said excitation element (1a,1b) and said first passive element (11a,11b) and having third conductive part and fourth conductive part; a first switch (12a, 12b) having two operating states of conduction and non-conduction, to switch between electrical connection between said first conductive part and second conductive part, and electrical non-connection between said first conductive part and second conductive part; and a second switch (22a,22b) having two operating states of conduction and non-conduction, to switch between electrical connection between said third conductive part and fourth conductive part, and electrical non-connection between said third conductive part and fourth conductive part; a first line extending in parallel with said first passive element (11a,11b) and connected to said second conductive part; a second line extending in parallel with said second passive element (21a,21b) and connected to said fourth conductive part; a third line connecting between said first conductive part and said third conductive part; and a fourth line connecting between said first line and said second line, and the antenna device further comprising: a controller to output an electric signal for controlling said conduction and said non-conduction of each of said first (12a,12b) and second (22a,22b) switches; a first dielectric substrate; and a second dielectric substrate secured with said first dielectric substrate; at a right angle wherein said excitation element (1a,1b) is disposed on one main surface of said first dielectric substrate, said first (11a,11b) and second (21a,21b) passive elements, said first (12a,12b) and second (22a,22b) switches, and said third line are disposed on one main surface of said second dielectric substrate, and said first, second and fourth lines are disposed on another main surface of said second dielectric substrate, and wherein said controller outputs an identical direct current signal, as said electric signal, to said first (12a,12b) and second (22a,22b) switches by applying a direct current signal between said third and fourth lines, and, when said identical direct current signal is outputted from said controller, one of said first (12a,12b) and second (22a,22b) switches is brought into conduction while the other one of said first and second switches is brought out of conduction. an element part including an excitation element (1a,1b) having a feed point for a radio frequency signal; a first passive element (11a, 11b) disposed at a position apart from said excitation element (1a,1b) and having first conductive part and second conductive part; a second passive element (21a,21b) disposed at a position apart from said excitation element (1a,1b) and said first passive element (11a,11b) and having third conductive part and fourth conductive part; a first switch (12a, 12b) having two operating states of conduction and non-conduction, to switch between electrical connection between said first conductive part and second conductive part, and electrical non-connection between said first conductive part and second conductive part; and a second switch (22a,22b) having two operating states of conduction and non-conduction, to switch between electrical connection between said third conductive part and fourth conductive part, and electrical non-connection between said third conductive part and fourth conductive part; a first line extending in parallel with said first passive element (11a,11b) and connected to said second conductive part; a second line extending in parallel with said second passive element (21a,21b) and connected to said fourth conductive part; a third line connecting between said first conductive part and said third conductive part; and a fourth line connecting between said first line and said second line, and the antenna device further comprising: a controller to output an electric signal for controlling said conduction and said non-conduction of each of said first (12a,12b) and second (22a,22b) switches; a first dielectric substrate; and a second dielectric substrate secured with said first dielectric substrate; a controller to output an electric signal for controlling said conduction and said non-conduction of each of said first (12a,12b) and second (22a,22b) switches; a first dielectric substrate; and a second dielectric substrate secured with said first dielectric substrate; at a right angle wherein said excitation element (1a,1b) is disposed on one main surface of said first dielectric substrate, said first (11a,11b) and second (21a,21b) passive elements, said first (12a,12b) and second (22a,22b) switches, and said third line are disposed on one main surface of said second dielectric substrate, and said first, second and fourth lines are disposed on another main surface of said second dielectric substrate, and wherein said controller outputs an identical direct current signal, as said electric signal, to said first (12a,12b) and second (22a,22b) switches by applying a direct current signal between said third and fourth lines, and, when said identical direct current signal is outputted from said controller, one of said first (12a,12b) and second (22a,22b) switches is brought into conduction while the other one of said first and second switches is brought out of conduction.