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; 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; and a storage unit for storing position information concerning the pattern extracted by the extracting unit, wherein the extracting unit extracts a renewed pattern on the surface of the measurement object, which differs from the pattern, from the image inside the imaging region in which the pattern exists, the storage unit stores a tracking displacement amount, which is a vector from a position of the pattern to a position of the renewed pattern, each time the renewed pattern is extracted, the measurement unit further measures the position on the surface of the measurement object based on each of a plurality of tracking displacement amounts stored in the storage unit, and the measurement unit measures the position on the surface of the measurement object based on the displacement amount, the dimension, and the position information stored by the storage unit.