An antenna device has a divider producing first and second signals, and amplifiers amplifying the signals at a changeable amplitude ratio of the first signal to the second signal. A Rotman lens gives first phase differences to first high frequency waves, produced from the first amplified signal at an input port and transmitted to output ports, and gives second phase differences to second high frequency waves produced from the second amplified signal at another input port and transmitted to the output ports. An antenna forms a beam composed of electromagnetic waves, having the first phase differences and electric power corresponding to the first amplified signal on an antenna surface, and electromagnetic waves, having the second phase differences and electric power corresponding to the second amplified signal on the antenna surface, and radiates the beam in a particular direction corresponding to the phase differences and the amplitude ratio.