A projection device of projecting an image on a screen is disclosed. A projection lens of the projection device is disposed between the screen and an imaging unit of the projection device, to project light from a light source of the projection device on the screen. The projection lens includes a first lens group and a second lens group. The first lens group adjacent to the screen includes a first lens, a second lens and a third lens having negative diopter. The first lens is an aspheric lens adjacent to the screen. The second lens group adjacent to the imaging unit has positive diopter. An effective focal length of the projection lens represents f, a focal length of the first lends group represents fG1, focal length of the first lens, the second lens and the third lens represents fL1, fL2 and fL3, and 0.75 ≤  f G   1  / f ≤ 1.28 ,  1 f L   1 + 1 f L   2  >  1 f L   3  .