This position measuring device comprising a calculation unit 19 calculates
mark position information relating to the position of the mark by using a
mark signal obtained by irradiating a detection beam onto the mark formed
on an object W, and a correction device 19 for correcting the calculation
results from the calculation unit 19 based on the asymmetry of the mark
signal.As a result, positional deviation resulting from asymmetry can be
detected, and by correcting for this deviation the effect that the image
asymmetry has on the measurement can be reduced. Therefore, a more
accurate high precision alignment can be performed, and there is no
requirement to increase the NA of the detection optical system, nor to
prepare a special short wavelength light source, meaning increases in the
size and cost of the apparatus can also be prevented.