A projection device includes: a light source module for generating an illumination beam; an optical engine module disposed on a transmission path of the illumination beam for forming an image beam; a projection lens disposed on a transmission path of the image beam for projecting the image beam to an outside of the projection device; and a housing having opposite bottom and top portions, and a side wall connected between and surrounding the portions and having an air inflow region adjacent to the bottom portion and an air exhaust region adjacent to the top portion. The light source module, the optical engine module and the projection lens are disposed in the housing adjacent to the top portion, wherein the image beam is projected to the outside toward the bottom portion. The projection device of the invention can effectively dissipate heat.