A three-dimensional printing apparatus including a tank filled with a liquid-state forming material, a platform disposed at the tank, a rotating shaft, a rotating arm, and at least one light source is provided. The rotating shaft is disposed under the tank or above the tank. The rotating arm connects to the rotating shaft such that the rotating arm is driven by the rotating shaft to rotate. The light source disposed on the rotating arm rotates along with the rotating arm and generates light projecting toward the forming material along with the part of the platform moving in the forming material, such that the forming material is solidified in layers and forms a three-dimensional object on the platform.