A disparity profile indicating a relation between a perpendicular position on time series images and a disparity on a target monitoring area based on an arrangement of a camera is calculated. Processing areas are set, by setting a height of each of the processing areas using a length at the bottom of the image obtained by converting a reference value of a height of an object according to the profile, while setting a position of each bottom of processing areas on the image. An object having a height higher than a certain height with respect to the monitoring area, unify an object detection result in each processing area according to the disparity of the object, and detect the object of the whole monitoring area from each processing area is detected. Position and speed for the object detected by the object primary detection unit are estimated.