A headlamp device of a straddle vehicle, the headlamp device comprising: at least one light source device; a reflector unit to which the at least one light source device is secured, the reflector unit having a reflecting surface by which light emitted from the at least one light source device is reflected forward; a power supply circuit board located behind the reflector unit to adjust a voltage of electric power to be supplied to the at least one light source device; a lamp housing accommodating the at least one light source device, the reflector unit, and the power supply circuit board; and an optical axis adjustment mechanism supporting the reflector unit in a manner permitting the reflector unit to tilt relative to the lamp housing, wherein the power supply circuit board is secured to the reflector unit, characterized in that: the at least one light source device includes a plurality of light source devices; the power supply circuit board is placed in a position where a normal to the power supply circuit board extends in a front-rear direction; the reflector unit comprises a pair of left and right light emission portions and a recess portion recessed from back to front of the reflector unit, the recess portion being located between the left and right light emission portions; and the power supply circuit board is shaped to be longer in an up-down direction than in a left-right direction and placed into the recess portion from behind. at least one light source device; a reflector unit to which the at least one light source device is secured, the reflector unit having a reflecting surface by which light emitted from the at least one light source device is reflected forward; a power supply circuit board located behind the reflector unit to adjust a voltage of electric power to be supplied to the at least one light source device; a lamp housing accommodating the at least one light source device, the reflector unit, and the power supply circuit board; and an optical axis adjustment mechanism supporting the reflector unit in a manner permitting the reflector unit to tilt relative to the lamp housing, wherein the power supply circuit board is secured to the reflector unit, characterized in that: the at least one light source device includes a plurality of light source devices; the power supply circuit board is placed in a position where a normal to the power supply circuit board extends in a front-rear direction; the reflector unit comprises a pair of left and right light emission portions and a recess portion recessed from back to front of the reflector unit, the recess portion being located between the left and right light emission portions; and the power supply circuit board is shaped to be longer in an up-down direction than in a left-right direction and placed into the recess portion from behind. the at least one light source device includes a plurality of light source devices; the power supply circuit board is placed in a position where a normal to the power supply circuit board extends in a front-rear direction; the reflector unit comprises a pair of left and right light emission portions and a recess portion recessed from back to front of the reflector unit, the recess portion being located between the left and right light emission portions; and the power supply circuit board is shaped to be longer in an up-down direction than in a left-right direction and placed into the recess portion from behind.