A projection device includes a light source emitting light beams, a display element displaying images according to video signals, an adjustable collimator arranged between the light source and the display element, and a condensing lens unit arranged between the adjustable collimator and the display element. The adjustable collimator collimates the light beams of the light source to parallel beams. The condensing lens projects the parallel beams to the display element. A driving unit is used for adjusting a distance between the light source and the adjustable collimator. A lens adjusting unit is used for adjusting a focus of the adjustable collimator according to the distance between the light source and the adjustable collimator. The projection device can reduce light loss and achieve a projection image with high contrast and high brightness.