A radar device for a vehicle includes a frequency analysis unit, a peak information acquisition unit, and a rainfall determination unit. The frequency analysis unit performs a two-dimensional fast Fourier transform on a beat signal, and the peak information acquisition unit extracts, from peaks of a power spectrum calculated by the two-dimensional fast Fourier transform, peaks within a predefined distance-velocity region preset as a raindrop condition, and acquire peak information. The rainfall determination unit determines whether a surrounding environment of the vehicle has rainfall, based on the peak information acquired by the peak information acquisition unit.