A headlight device for a vehicle, comprising: a first lamp unit (21 OR) that forms: a first low beam light distribution pattern (Lo) including a cutoff line; and a first plurality of types of additional light distribution patterns (RHi1, RHi2, RHi3) each including a first oblique cutoff line (RCL1, RCL2, RCL3), wherein each of the first oblique cutoff lines (RCL1, RCL2, RCL3) extends upwardly in a vehicle width direction toward the outside in an opposite lane region above the cutoff line of the first low beam light distribution pattern (Lo), and wherein the inclination angles of the first oblique cutoff lines (RCL1, RCL2, RCL3) are different from one another; a second lamp unit that forms: a second low beam light distribution pattern including a cutoff line; and a second plurality of types of second additional light distribution patterns (LHi1, LHi2, LHi3) each including a second oblique cutoff line (LCL1, LCL2, LCL3), wherein each of the second oblique cutoff lines (LCL1, LCL2, LCL3) extends upwardly in the vehicle width direction toward the outside in a travelling lane region above the cutoff line of the second low beam light distribution pattern, and wherein the inclination angles of the second oblique cutoff lines (LCL1, LCL2, LCL3) are different from one another, and a controller that controls the switching of the first and/or second additional light distribution patterns (RHi1, RHi2, RHi3; LHi1, LHi2, LHi3) in accordance with a situation of a forward vehicle in front of the vehicle, and characterized in that the additional light distribution patterns of the first lamp unit and the second lamp unit remain unchanged in the travelling lane region and the opposite lane region, respectively. a first lamp unit (21 OR) that forms: a first low beam light distribution pattern (Lo) including a cutoff line; and a first plurality of types of additional light distribution patterns (RHi1, RHi2, RHi3) each including a first oblique cutoff line (RCL1, RCL2, RCL3), wherein each of the first oblique cutoff lines (RCL1, RCL2, RCL3) extends upwardly in a vehicle width direction toward the outside in an opposite lane region above the cutoff line of the first low beam light distribution pattern (Lo), and wherein the inclination angles of the first oblique cutoff lines (RCL1, RCL2, RCL3) are different from one another; a first low beam light distribution pattern (Lo) including a cutoff line; and a first plurality of types of additional light distribution patterns (RHi1, RHi2, RHi3) each including a first oblique cutoff line (RCL1, RCL2, RCL3), wherein each of the first oblique cutoff lines (RCL1, RCL2, RCL3) extends upwardly in a vehicle width direction toward the outside in an opposite lane region above the cutoff line of the first low beam light distribution pattern (Lo), and wherein the inclination angles of the first oblique cutoff lines (RCL1, RCL2, RCL3) are different from one another; a second lamp unit that forms: a second low beam light distribution pattern including a cutoff line; and a second plurality of types of second additional light distribution patterns (LHi1, LHi2, LHi3) each including a second oblique cutoff line (LCL1, LCL2, LCL3), wherein each of the second oblique cutoff lines (LCL1, LCL2, LCL3) extends upwardly in the vehicle width direction toward the outside in a travelling lane region above the cutoff line of the second low beam light distribution pattern, and wherein the inclination angles of the second oblique cutoff lines (LCL1, LCL2, LCL3) are different from one another, and a second low beam light distribution pattern including a cutoff line; and a second plurality of types of second additional light distribution patterns (LHi1, LHi2, LHi3) each including a second oblique cutoff line (LCL1, LCL2, LCL3), wherein each of the second oblique cutoff lines (LCL1, LCL2, LCL3) extends upwardly in the vehicle width direction toward the outside in a travelling lane region above the cutoff line of the second low beam light distribution pattern, and wherein the inclination angles of the second oblique cutoff lines (LCL1, LCL2, LCL3) are different from one another, and a controller that controls the switching of the first and/or second additional light distribution patterns (RHi1, RHi2, RHi3; LHi1, LHi2, LHi3) in accordance with a situation of a forward vehicle in front of the vehicle, and characterized in that the additional light distribution patterns of the first lamp unit and the second lamp unit remain unchanged in the travelling lane region and the opposite lane region, respectively.