The parts of a garment are arranged at the periphery of a model of the human body, interference between the parts of the garment and the model of the human body is detected, and the interfering parts of the garment are separated from the model of the human body to eliminate the interference. A joining line is positioned between two parts of the garment which are to be joined together, and the ends of these parts are moved towards the joining line. If the end of a part of the garment comes into contact with the model of the human body while moving, the part is deflected. Then, the joining lineis moved so as to accommodate the parts after the parts have been moved, and these movements are repeated until the joining line is in contact with the ends of the parts of the garment. Subsequently,the fit of the garment is simulated, taking into account the strain in the garment, gravity and interference with the model of the human body. Thus, it is easy to dispose the parts of the garment at the periphery of the model of the human body, and the parts of the garment can be joined in a natural state.