A steering assistant includes a lane width setting unit and a determination unit. The lane width setting unit provides setting of a lane width between lane lines on right and left sides of an own vehicle. The determination unit monitors a lane line state to determine how the lane line state has transited, in which the lane line state involves presence or absence of the lane lines on the right and left sides of the own vehicle. The lane width setting unit provides the setting of the lane width, with a virtual lane line assumed on side on which the lane line is missing, when it is determined that the lane line state has transited to a state in which the lane line is provided on either one of the right and left sides of the own vehicle.
