The present invention relates to a radar device for a vehicle which may determine a target as a single target or multiple targets according to a dispersion level of a slope for each reception channel, calculated through a phase difference for each reception channel of a reflection signal and an arrangement interval for each reception channel, and estimate the angle of the target so as to acquire the angle of the target using a small amount of calculations, and a method for estimating the angle of a target using the same. An embodiment of the present invention provides a radar device for a vehicle, which detects a target located in the front side of a vehicle, comprising an electronic control unit configured to: calculate the slope of a reflection signal received for each reception channel, using a phase difference for each reception channel of the reflection signal and an arrangement interval for each reception channel, wherein the reflection signal is obtained by transmitting a predetermined transmission signal and receiving the transmitted transmission signal which is reflected back from the target; and determine the target as a single target or multiple targets according to a dispersion level of the calculated slope so as to estimate the angle to the determined target.