A downlight apparatus includes a unibody housing, a light source, a light source plate, a first fixing unit, a lens module and a second fixing unit. The unibody housing is made of metal material. The unibody housing has a light source holder and a heat sink rim. The heat sink rim has a top edge and a bottom edge. The top edge is connected to the light source holder. The top edge has a smaller diameter than the bottom edge. The light source plate is used for mounting the light source. The lens module is fixed between the first fixing unit and the second fixing unit to align a center of the lens module with the light source. The second fixing unit is fixed to a peripheral edge of the light source holder for keeping the lens module, and the light source plate staying in the light source holder.