An in-vehicle radar apparatus includes an interference determination means, a selection means, and a frequency changing means. The interference determination means determines presence or absence of interference between multifrequency CWs, which are radar waves, based on a beat signal generated by mixing a transmission signal and a received signal, which are radar waves. The selection means selects an own vehicle or an other-side apparatus, which is a party of the interference, according to an occurrence state of the interference, when the interference determination means determines that the interference is present. The frequency changing means that changes a center frequency of the multifrequency CW transmitted from the own vehicle, when the selection means selects the own vehicle.