An additive manufacturing method for preparing a built-up object by depositing a bead formed by melting and solidifying a filler metal on a base, the method comprising: a step of reading three-dimensional shape data of the built-up object; a step of determining a deposition direction of the bead depending on a three-dimensional model shape of the three-dimensional shape data; a step of dividing the three-dimensional model shape into a plurality of layers along the deposition direction; a step of dividing each layer, that is divided, into a bead model of a plurality of lines depending on a bead shape in a formation order of the bead; and a step of preparing the built-up object by repeating a process of forming the bead along the bead model from a lower layer to an upper layer of the plurality of layers, wherein, in the step of dividing into the bead model of the plurality of lines, to a position where the bead is formed in a portion not adjacent to an existing bead in the layer, a trapezoidal bead model a vertical cross section of which in a bead longitudinal direction is a trapezoidal shape is applied, in the trapezoidal bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in a bead arrangement direction in the layer being non-parallel to each other, and, to a position where the bead is formed adjacent to a bead that is already formed, a parallelogram bead model a vertical cross section of which in the bead longitudinal direction is a parallelogram is applied, in the parallelogram bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in the bead arrangement direction being parallel to a side of another bead model that is adjacent. a step of reading three-dimensional shape data of the built-up object; a step of determining a deposition direction of the bead depending on a three-dimensional model shape of the three-dimensional shape data; a step of dividing the three-dimensional model shape into a plurality of layers along the deposition direction; a step of dividing each layer, that is divided, into a bead model of a plurality of lines depending on a bead shape in a formation order of the bead; and a step of preparing the built-up object by repeating a process of forming the bead along the bead model from a lower layer to an upper layer of the plurality of layers, wherein, in the step of dividing into the bead model of the plurality of lines, to a position where the bead is formed in a portion not adjacent to an existing bead in the layer, a trapezoidal bead model a vertical cross section of which in a bead longitudinal direction is a trapezoidal shape is applied, in the trapezoidal bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in a bead arrangement direction in the layer being non-parallel to each other, and, to a position where the bead is formed adjacent to a bead that is already formed, a parallelogram bead model a vertical cross section of which in the bead longitudinal direction is a parallelogram is applied, in the parallelogram bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in the bead arrangement direction being parallel to a side of another bead model that is adjacent. to a position where the bead is formed in a portion not adjacent to an existing bead in the layer, a trapezoidal bead model a vertical cross section of which in a bead longitudinal direction is a trapezoidal shape is applied, in the trapezoidal bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in a bead arrangement direction in the layer being non-parallel to each other, and, to a position where the bead is formed adjacent to a bead that is already formed, a parallelogram bead model a vertical cross section of which in the bead longitudinal direction is a parallelogram is applied, in the parallelogram bead model opposite sides in the deposition direction of the bead being parallel to each other, and opposite sides in the bead arrangement direction being parallel to a side of another bead model that is adjacent.