On the +X and −X sides of a projection unit, a plurality of Z heads are arranged in parallel to the X-axis, by a predetermined distance half or less than half the effective width of the Y scale so that two Z heads each constantly form a pair and face a pair of Y scales. Of the pair of heads consisting of two Z heads which simultaneously face the scale, measurement values of a priority head is used, and when abnormality occurs in the measurement values of the priority head due to malfunction of the head, measurement values of the other head is used, and the positional information of the stage in at least the Z-axis direction can be measured in a stable manner and with high precision.