An apparatus for detecting an object, includes: a candidate point detection unit detecting a candidate point between the ground and an object from an image; a tracking unit calculating positions of the candidate point at a first time and a second time; a difference calculation unit calculating a difference between an estimated position at the second time and the candidate point position at the second time; and a state determination unit determining a new state of the candidate point at the second time based on the difference, and changing the search threshold value or a state.