An active energy radiation unit includes a light source which radiates ultraviolet rays onto a target object, and a main gas supply mechanism which is disposed to be adjacent to the light source and ejects an inert gas. The main gas supply mechanism includes a receiving part which receives the inert gas, and a main ejection port which is provided at a position between the receiving part and the light source and closer to the target object than the receiving part. A flow path area from the receiving part to the main ejection port is constant.