A building time for building an additively-manufactured object is calculated on the basis of the inter-pass time and the welding pass time and is compared with a preset upper limit value, and welding conditions in a depositing plan are repeatedly modified until the building time is equal to or less than the upper limit value. Alternatively, corrections are repeatedly performed until the shape difference between a building shape of built-up object shape data relating to the additively-manufactured object created on the basis of the inter-pass time and the inter-pass temperature, and a building shape of three-dimensional shape data, is smaller than a near net value.