A position detecting method for detecting the position of a substrate by use of a grating pattern provided on the substrate includes irradiating the grating pattern with first and second radiation beams having different wavelengths to produce first and second diffraction beams of different wavelengths; and receiving the first and second diffraction beams by use of a sensor to determine the position of the substrate on the basis of the position of incidence of each of the first and second diffraction beams on the sensor.