A surface position measuring method wherein measurement light is obliquely projected onto a substrate surface and on the basis of a position of the detected measurement light and a predetected offset, the position of the substrate surface with respect to a direction of an optical axis of the projection optical system is measured, memorizing a first position of a point on the substrate while using a reference mark provided on a substrate stage, measuring the position of the measurement light as a first measurement position; rotating the substrate by 180 deg. in a plane perpendicular to the optical axis; memorizing a second position of the measurement point on the rotated substrate with reference to the reference mark; measuring the position of the measurement light as a second measurement position; and detecting of the offset at the measurement point on the basis of the first and second measurement position.