A three-dimensional printing apparatus includes a projector to project a first image onto a tank and a controller to control the projector. The controller includes an acquirer, an inclination calculator, a vertical and horizontal correction value calculator, a memory, and a corrector. The acquirer projectively transforms the first image, thus acquiring a second image obtained by correction of the first image. The second image includes a projection sub-image. The inclination calculator calculates horizontal and vertical inclinations of the projection sub-image in the second image. The vertical and horizontal correction value calculator calculates a first correction value based on the horizontal inclination, and calculates a second correction value based on the vertical inclination. The memory stores a third correction value. The corrector corrects the brightness distribution of the second image using a fourth correction value calculated based on the first to third correction values.