The capacity of respective vitreous silica crucible is grasped precisely to predict the initial liquid surface level of the silicon melt in the vitreous silica crucible. Thereby the dipping process of the seed crystal is reliably performed. Spatial coordinates of multiple points on an inner surface of the vitreous silica crucible prior to filling raw material in the vitreous silica crucible, and a three-dimensional shape of the inner surface of the vitreous silica crucible from a combination of polygons having each measurement point as a vertex coordinate is specified (S11); a predictive value of an initial liquid surface level of the silicon melt in the vitreous silica crucible is preset (S12); a volume of the silicon melt satisfying the predictive value of the initial liquid surface level is obtained based on the three-dimensional shape of the inner surface of the vitreous silica crucible (S13); a weight of the silicon melt having the volume is obtained (S14); raw material having the weight is filled in the vitreous silica crucible (S15); a dipping control of the seed crystal is performed based on the predictive value of the initial liquid surface level (S17).