1. A vehicle control device for controlling driving of a vehicle based on recognition of a lane marker existing in a road environment in front of the vehicle driving on a lane, the vehicle control device comprising: a vehicle controller; a recognition section configured to recognize a three dimensional object provided alongside the lane in which the vehicle is positioned; and an imaginary line setting section configured to set an imaginary line based on the three dimensional object recognized by the recognition section and to treat the imaginary line as the lane marker, wherein, when the road environment includes a guardrail provided facing the three dimensional object in a direction across the lane, the recognition section recognizes a plurality of three dimensional object points existing in the three dimensional object and recognizes a plurality of installation points included in the guardrail, and the imaginary line setting section configured to: find a first straight line based on an approximate straight line connecting the three dimensional object points; setting an imaginary line candidate at a position a first distance away from the first straight line toward a side of the vehicle, which is the position between the three dimensional object and the vehicle; finding a second straight line based on an approximate straight line connecting the installation points; moving the second straight line by a second distance to the imaginary line candidate side in the direction across the lane; and correcting the position of the imaginary line candidate based on the moved second straight line so as to set the imaginary line, and the vehicle controller is configured to control the driving of the vehicle based on the corrected imaginary line recognized as the lane marker.