1. A pedestrian detection apparatus for detecting pedestrians about a vehicle comprising: an image generator for capturing images of an environment of the vehicle to generate and deliver image outputs; a sensor for sensing obstacles about the vehicle and delivering distance data between the obstacles and the vehicle; a critical area detector for generating polylines by clustering a plurality of the distance data and classifying obtained polylines according to their size and shape into multiple categories in order to detect multiple categories of obstacles; and a pedestrian detector for detecting the pedestrians preferentially from images corresponding to the critical areas.