A head lamp device of a straddle vehicle, the head lamp device having an optical axis adjustment mechanism, comprises a housing; and an internal unit including a light source device which emits light, and a light output device which outputs in a forward direction the light emitted from the light source device, through the housing, the internal unit being accommodated in the housing in a state in which the internal unit is tiltable with respect to the housing. The internal unit includes a support point part which is tiltably supported by the housing. In a front view, the support point part is disposed in an area center of the internal unit or at a location that is in the vicinity of the area center.