To accurately calculate the housing attitude of a wafer always independent of errors in mounting light emitting devices or a change of light emitting devices in position with time by a method wherein the attitude of each wafer is judged from the inclination of a optical beam and the position of each wafer.

A carrier 2 where wafers 1 are housed is mounted on a carrier mounding pad 7, the carrier mounting pad 7 is driven in a vertical direction, the position data of knife edges 9b and 10b and the wafers 1 are sampled through the output. of optical beams 11a and 11b (step 12), an inclination of the optical beams 11a and 11b is calculated from the position data of the knife edges 9b and 10b (step 13). Then, reference shading widths Sa and Sb and a driving distance hc of a loading/unloading hand 3 to an insertion station are calculated from data concerning the inclination of the optical beams 11a and 11b and the diameter of the wafers 1. By this setup, the attitude of wafers can be accurately obtained independent of an error or a change in an angle of an optical beam with time.