LANE BOUNDARY DETECTOR

A boundary detector includes a candidate line detecting unit that detects a candidate line of a lane boundary position drawn on a road surface based on image data of a predetermined detection time period acquired from a camera. The detector also includes a lane boundary position selecting unit that selects a lane boundary position based on the candidate line; a branch lane boundary position selecting unit that selects a lane boundary position of a branch lane that diverts from a main lane based on the candidate line; and a branch processing unit that sets a branch process mode in which the detection time period is short without using the selected lane boundary position of the branch lane when the branch lane boundary position selecting unit selects the lane boundary position of the branch lane.