The invention relates to a light distribution control method and a light distribution control device in which plural illumination regions are arranged in the left-right direction and illuminated by a headlamp in an ADB light distribution pattern, and vehicle positions of a vehicle ahead are detected and selected ones of the plural illumination regions are reduced in light quantity according to the detected vehicle positions. In this method and device, corrected vehicle positions are set that are obtained by adding margins to the detected vehicle positions in the left and right directions, respectively, and compared with the plural illumination regions. Illumination regions where the vehicle ahead exists are reduced in light quantity.