A lane information detection unit detects the shape and the road width of a traveling lane of a vehicle. A present transverse position detection unit detects a present transverse position indicating a present traveling position of the vehicle in the width direction of the traveling lane. A driver-corresponding transverse position setting unit sets a driver-corresponding transverse position corresponding to a driving tendency of a driver. An upper/lower limit value setting unit sets upper/lower limit values that the driver-corresponding transverse position can take, in accordance with the road width. Then, when change in the road width is detected, a transverse position control amount calculation unit sets, as a target transverse position, the driver-corresponding transverse position within the upper/lower limit values in which the change is reflected, and calculates a transverse position control amount for the vehicle from the present transverse position of the vehicle.