An antenna for vehicles includes a first AGC unit and a second AGC unit. The first AGC unit determines the strength of a signal, which is input to the input stage of an amplifier without passing through a transistor. Depending on the determination result, the first AGC unit attenuates the signal and output the attenuated signal to the transistor. When a signal having a value equal to or greater than a reference value is input to the input stage, the second AGC unit operates so as to output the signal without passing through the transistor. According to the antenna, both signals in a strong electric field area and signals in a weak electric field area close to the strong electric field area can be effectively controlled.