A lane determining device includes: a feature information obtaining unit for obtaining feature information F of a target feature existing in each lane in the traveling direction of a vehicle 30, based on vehicle position information; an image recognizing unit for conducting image recognition processing of a feature type of the target feature in a vehicle lane, with respect to image information; and a lane accuracy determining unit for determining a vehicle lane accuracy for the respective lanes based on a type of a recognized feature fa shown in an image recognition result, feature types Ft1 to Ft4 of the target feature of the respective lanes shown in the feature information F, in accordance with a level of probability for each of the feature types Ft1 to Ft4 of the target feature of the respective lanes is recognized as the type of the recognized feature fa.