Disclosed herein is an installation angle distinction apparatus including at least: an Input unit which inputs a current relative distance value, current relative velocity value and current horizontal angle value of a stationary object; an estimation unit which estimates a vertical height of the stationary object, and estimates vertical height values of the stationary object at each of predetermined time points for different distances and estimates a current vertical installation angle value of the detector; a determination unit which determinates that the current vertical installation angle of the detector is abnormal when the estimated current vertical installation angle value is deviated from a reference vertical installation angle value range preset; and a control unit which receives the current relative distance value, the current relative velocity value, and the current horizontal angle value, transmits an estimation command and a determination command to the estimation unit the determination unit, respectively.