Provided is a three-dimensional deposition device, including: a powder supply unit which supplies a powder material; a light irradiation unit which irradiates the powder material with a light beam so that the powder material irradiated with the light beam is sintered or melted and solidified to form a formed layer; a three-dimensional deposition chamber which is sealed from an outside and accommodates the powder supply unit, the light irradiation unit, and a base unit; a gas discharge unit which discharges a gas inside the three-dimensional deposition chamber; and a gas introduction unit which introduces a predetermined gas into the three-dimensional deposition chamber. When the gas discharge unit discharges a gas inside the three-dimensional deposition chamber and the gas introduction unit introduces a predetermined gas thereinto, a predetermined gas atmosphere is formed inside the three-dimensional deposition chamber.