1. An alignment method for sequentially aligning a plurality of alignment targets formed on a substrate, in a predetermined configuration, to a predetermined reference position, the method comprising: a first step of sequentially measuring the positions of a plurality of sample targets selected from the alignment targets; a second step of calculating conversion parameters which represent an amount of position correction required for each of the sample targets so as to minimize an overall error between the measured positions and designed positions of the sample targets; a third step of additionally selecting at least one sample target from the alignment targets and measuring the position of each of the selected sample targets; a fourth step of calculating conversion parameters which represent an amount of position correction required for each of the sample targets so as to minimize an overall error between the measured positions, including (i) the measured positions obtained in the third step and (ii) the designed positions of the sample targets; and a fifth step of determining whether to finish the alignment measurement on the basis of a plurality of sets of conversion parameters.