The disclosure provides a three-dimensional (3D) printing device including a tank, a forming stage and an irradiation unit. The tank is filled with a liquid forming material. The forming stage is movably disposed at the tank. The irradiation unit is disposed beside the tank and includes an image source and a projecting lens. The image source is used to emit an image beam. The image beam passes through the projecting lens to irradiate and cure the liquid forming material. An entrance pupil position of the projecting lens is ENP and 2000 mm≤ENP≤15000 mm. An exit pupil position of the projecting lens is EXP and 2000 mm≤|EXP|≤15000 mm.