A three-dimensional printer includes a projector, a tank, and a platform. The projector includes a light source, a digital micromirror device, and a controller. The digital micromirror device includes a micromirror, and the micromirror may be switched between an on state and an off state according to a control signal. The controller is electrically connected to the digital micromirror device and the light source. The controller further includes a judgement unit. The judgement unit may output the control signal to switch the micromirror to the off state when the light source is in the off state. The platform is adjacent to the tank. In addition, a manufacturing method for a three-dimensional printer is provided.