1. A radar device for scanning a predetermined angle range centered on a predetermined reference direction, comprising: a target position detection unit which detects a position of a target within the angle range, on an XY coordinate plane having the reference direction as a Y-axis and a direction perpendicular to the reference direction as an X-axis, for each scanning; and a target position estimation unit which, on a scan in which the target position is not detected, obtains a trajectory of the target on the basis of a first position of the target detected previously and a second position detected after the detection of the first position, and estimates a position having an X coordinate shifted by a first displacement from the X coordinate of the second position to be a position for detection by the scan when the trajectory is within a predetermined region in the vicinity of the Y-axis, and estimates a position having an X coordinate shifted by a second displacement larger than the first displacement from the X coordinate of the second position to be a position for detection by the scan when the trajectory is not within the predetermined region.