A vehicular headlamp apparatus comprising: a lamp body that has an opening section at a vehicle front side; a translucent cover that is attached so as to cover the opening section; and a lamp unit that is provided in a lamp chamber defined by the lamp body and the translucent cover, and that includes a light source mounting portion, a semiconductor light-emitting element that serves as a light source and a reflector that has a reflective surface reflecting light, irradiated from the semiconductor light-emitting element, toward a vehicle front, wherein the translucent cover has a slanted portion that is slanted with respect to a plane perpendicular to an optical axis of the lamp unit, the optical axis extending in a vehicle longitudinal direction, the semiconductor light-emitting element is mounted on the light source mounting portion so that an irradiation axis of the semiconductor light-emitting element intersects with the optical axis of the lamp unit, one end (16a1) of the reflective surface is located on a vehicle rear side with respect to the semiconductor light-emitting element, the other end (16a2) of the reflective surface protrudes toward the vehicle front from a vehicle front side end of the light source mounting portion, the reflective surface has a portion (16a3) that protrudes toward the vehicle front from the vehicle front side end of the light source mounting portion to face the slanted portion, whereby the vehicular headlamp apparatus being characterised in that said reflective surface comprises a first area, a second area that is located adjacent to the first area and a third area wherein the first area includes a portion that intersects with a plane that includes the optical axis and the irradiation axis, light reflected by the first area forms a horizontal cut-off line within a light distribution pattern, light reflected by the second area forms an oblique cut-off line within the light distribution pattern, and light reflected by the third area forms a diffusion portion within the light distribution pattern. a lamp body that has an opening section at a vehicle front side; a translucent cover that is attached so as to cover the opening section; and a lamp unit that is provided in a lamp chamber defined by the lamp body and the translucent cover, and that includes a light source mounting portion, a semiconductor light-emitting element that serves as a light source and a reflector that has a reflective surface reflecting light, irradiated from the semiconductor light-emitting element, toward a vehicle front, wherein the translucent cover has a slanted portion that is slanted with respect to a plane perpendicular to an optical axis of the lamp unit, the optical axis extending in a vehicle longitudinal direction, the semiconductor light-emitting element is mounted on the light source mounting portion so that an irradiation axis of the semiconductor light-emitting element intersects with the optical axis of the lamp unit, one end (16a1) of the reflective surface is located on a vehicle rear side with respect to the semiconductor light-emitting element, the other end (16a2) of the reflective surface protrudes toward the vehicle front from a vehicle front side end of the light source mounting portion, the reflective surface has a portion (16a3) that protrudes toward the vehicle front from the vehicle front side end of the light source mounting portion to face the slanted portion, whereby the vehicular headlamp apparatus being characterised in that said reflective surface comprises a first area, a second area that is located adjacent to the first area and a third area wherein the first area includes a portion that intersects with a plane that includes the optical axis and the irradiation axis, light reflected by the first area forms a horizontal cut-off line within a light distribution pattern, light reflected by the second area forms an oblique cut-off line within the light distribution pattern, and light reflected by the third area forms a diffusion portion within the light distribution pattern.