An interference determination method for machine tools which determines whether or not there will be interference between elements that move relative to each other, the method including: a setting procedure for setting a machine tool model (MA) obtained by combining the shape model (M) of each of the elements including a work model (M1) corresponding to the work (W); a measurement procedure for measuring the position of the work (W) attached to the work attachment part (4); a correction procedure for acquiring, at a predetermined timing, the position of the work (W) measured in the measurement procedure, and correcting the machine tool model (MA) set in the setting procedure; and a determination procedure for determining whether or not there will be interference between the elements on the basis of the machine tool model (MA') corrected in the correction procedure.