An optical unit for a vehicle headlamp, comprising: a light source having a plurality of light-emitting elements disposed in an array; a rotary reflector structured to rotate while reflecting light emitted from the light source; and a controller for controlling an on state of the plurality of light-emitting elements, wherein the rotary reflector includes a reflective surface provided to form a light-distribution pattern by scanning light reflected by the rotating rotary reflector as a light source image, wherein the plurality of light-emitting elements include a first light-emitting element (S11-S15), a second light-emitting element (S21-S29), and a third light-emitting element (S31-S32), the first light-emitting element arranged for forming a low beam light-distribution pattern that irradiates a range below a horizontal line, the second light-emitting element arranged for forming a high beam light-distribution pattern that irradiates at least a range above the horizontal line, and the third light-emitting element being so disposed as to scan a region that overlaps a region that the first light-emitting element scans and a region that the second light-emitting element scans, in the light source, the first light-emitting element (S11-S15) and the second light-emitting element (S21-S29) are arrayed in a direction intersecting a direction in which the light is scanned as the light source image, and characterized in that the controller is structured to control the on state of the first light-emitting element, the second light-emitting element and the third light-emitting element such that an on duration T1 of the first light-emitting element arranged for forming the low beam light-distribution pattern, an on duration T2 (T2 > 0) of the second light-emitting element arranged for forming the high beam light-distribution pattern and on duration T3 of the third light-emitting element satisfy T1 > T3 > T2 and T2 > 0, so that the light-distribution pattern has a cutoff line across the horizontal line on a host vehicle's lane side that rises obliquely or stepwise toward an outer side. a light source having a plurality of light-emitting elements disposed in an array; a rotary reflector structured to rotate while reflecting light emitted from the light source; and a controller for controlling an on state of the plurality of light-emitting elements, wherein the rotary reflector includes a reflective surface provided to form a light-distribution pattern by scanning light reflected by the rotating rotary reflector as a light source image, wherein the plurality of light-emitting elements include a first light-emitting element (S11-S15), a second light-emitting element (S21-S29), and a third light-emitting element (S31-S32), the first light-emitting element arranged for forming a low beam light-distribution pattern that irradiates a range below a horizontal line, the second light-emitting element arranged for forming a high beam light-distribution pattern that irradiates at least a range above the horizontal line, and the third light-emitting element being so disposed as to scan a region that overlaps a region that the first light-emitting element scans and a region that the second light-emitting element scans, in the light source, the first light-emitting element (S11-S15) and the second light-emitting element (S21-S29) are arrayed in a direction intersecting a direction in which the light is scanned as the light source image, and characterized in that the controller is structured to control the on state of the first light-emitting element, the second light-emitting element and the third light-emitting element such that an on duration T1 of the first light-emitting element arranged for forming the low beam light-distribution pattern, an on duration T2 (T2 > 0) of the second light-emitting element arranged for forming the high beam light-distribution pattern and on duration T3 of the third light-emitting element satisfy T1 > T3 > T2 and T2 > 0, so that the light-distribution pattern has a cutoff line across the horizontal line on a host vehicle's lane side that rises obliquely or stepwise toward an outer side.