1. A position measurement apparatus in which an image capturing element having an imaging region of a dimension smaller than that of a measurement object is moved relatively over a surface of the measurement object while an image on the surface of the measurement object is captured to obtain an image inside the imaging region, and a position on the surface of the measurement object is measured using the obtained image inside the imaging region, comprising: an extracting unit for extracting a pattern on the surface of the measurement object from the image inside the imaging region at a predetermined point in time; a detector for detecting a displacement amount of the pattern extracted by the extracting unit occurring in the image inside the imaging region at a point in time after the predetermined point in time; and a measurement unit for measuring the position on the surface of the measurement object based on the dimension and the displacement amount detected by the detector.