A radar device is disclosed, which includes an antenna for transmitting an electromagnetic wave and receiving an echo signal from a target object while rotating in a horizontal plane, a display module for displaying the target object so as to correspond the echo signal to a position of the target object with respect to the antenna, a speed calculation module for calculating a relative velocity of the antenna and the target object, and a risk level detection module for detecting a risk level of the target object based on the relative velocity of the target object calculated by the speed calculation module. The speed calculation module calculates the relative velocity of the target object based on a change in phases of at least two of the echo signals received at a different time. The display module controls a display mode of the target object based on the risk level.