1. An obstacle detecting apparatus, comprising: a stereo camera which photographs a front of a vehicle to generate a left image and a right image; an image matching unit which applies a block matching algorithm to the left image and the right image to extract a plurality of feature points having a similarity which is equal to or larger than a reference value and calculate a coordinate and a depth of the plurality of extracted feature points; a plane calculating unit which connects every three feature points of the plurality of feature points to calculate a plurality of triangles, based on the coordinate and the depth of the plurality of feature points; a normal calculating unit which calculates directions of normal of the plurality of triangles, based on the coordinate and the depth of three feature points corresponding to vertexes of the plurality of triangles; and an obstacle detecting unit which detects an obstacle in front of the vehicle based on a result of comparing a photographing direction of the stereo camera with the normal directions of the plurality of triangles.