A dart designing method for designing with the use of a designing unit a garment by three-dimensionally simulating a worn state of the garment on a human body model and displaying an image obtained by the simulation, on a color monitor, the dart designing method comprising: a generation step of generating, on the garment, a plurality of positions where darts (45, 46, 51 to 55, 70 to 76) are to be formed; a distance calculation step of obtaining a distance between the garment and the human body model in each of the positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed; a perimeter calculation step of obtaining a difference between a perimeter of the garment and a perimeter of the human body model, along the plurality of positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed; a width determination step of determining a width of each of the darts (45, 46, 51 to 55, 70 to 76), such that the width of each of the darts (45, 46, 51 to 55, 70 to 76) increases as the distance between the garment and the human body model increases in each of the positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed, and that the width of each of the darts (45, 46, 51 to 55, 70 to 76) increases as the perimeter difference increases; and a length determination step of determining a length of each of the darts (45, 46, 51 to 55, 70 to 76), such that each of the darts (45, 46, 51 to 55, 70 to 76) is extended along an axial direction of the human body model, and that a point, on an extended line of each of the darts (45, 46, 51 to 55, 70 to 76), where the distance between the garment and the human body model is equal to or shorter than a predetermined value, is set as an end point of each of the darts (45, 46, 51 to 55, 70 to 76), the designing unit designing the darts (45, 46, 51 to 55, 70 to 76) in the garment, such that each of the positions generated in the generation step has the width determined in the width determination step, and that the point obtained in the length determination step is set as the end point. a generation step of generating, on the garment, a plurality of positions where darts (45, 46, 51 to 55, 70 to 76) are to be formed; a distance calculation step of obtaining a distance between the garment and the human body model in each of the positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed; a perimeter calculation step of obtaining a difference between a perimeter of the garment and a perimeter of the human body model, along the plurality of positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed; a width determination step of determining a width of each of the darts (45, 46, 51 to 55, 70 to 76), such that the width of each of the darts (45, 46, 51 to 55, 70 to 76) increases as the distance between the garment and the human body model increases in each of the positions where the darts (45, 46, 51 to 55, 70 to 76) are to be formed, and that the width of each of the darts (45, 46, 51 to 55, 70 to 76) increases as the perimeter difference increases; and a length determination step of determining a length of each of the darts (45, 46, 51 to 55, 70 to 76), such that each of the darts (45, 46, 51 to 55, 70 to 76) is extended along an axial direction of the human body model, and that a point, on an extended line of each of the darts (45, 46, 51 to 55, 70 to 76), where the distance between the garment and the human body model is equal to or shorter than a predetermined value, is set as an end point of each of the darts (45, 46, 51 to 55, 70 to 76), the designing unit designing the darts (45, 46, 51 to 55, 70 to 76) in the garment, such that each of the positions generated in the generation step has the width determined in the width determination step, and that the point obtained in the length determination step is set as the end point.