The invention provides a projection device including a housing, a light source module, an optical engine module, and a projection lens. The light source module includes a light source and a light source heat dissipation module. The light source heat dissipation module includes a light source dissipation fin. The optical engine module is located on a light transmission path of a light emitted from the light source. The optical engine module includes a light-modulating device and an optical engine dissipation fin. An extension direction of a supporting surface of the light-modulating device is parallel to an upper casing or an lower casing of the housing. The optical engine dissipation fin is disposed above the supporting surface of the light-modulating device. The light-modulating device is located between the optical engine dissipation fin and the light source dissipation fin. The projection lens is connected to the optical engine module.