A method is provided for measuring a shift between a carrier for a pattern (a carrier plate) and a flask and preventing a defect caused by a shift in the cavity parts. The method for preventing a defect caused by the shift in the cavity parts in molding a cope and a drag with flasks by using a cope flask (110) that is assembled with a carrier plate (130) for the cope flask and a drag flask (120) that is assembled with a carrier plate (140) for the drag flask, comprises the steps of measuring a shift between the carrier plate (130) for the cope flask and the cope flask (110), measuring a shift between the carrier plate (140) for the drag flask and the drag flask (120), measuring a shift between the cope flask (110) and the drag flask (120) that have been assembled, determining if a shift in cavity parts is within an allowable range, wherein the data on the shift is obtained based on the shift between the carrier plate (130) for the cope flask and the cope flask (110), the shift between the carrier plate (140) for the drag flask and the drag flask (120), and the shift between the cope flask (110) and the drag flask (120, that have been assembled.