In the epitaxial growth process in which each growth region D is zoned by a mask 2 formed in grid pattern, because a consumption region C of the Group III nitride compound semiconductor is formed in the central portion of each band of the mask 2 between each adjacent edge portion of the growth region D, Group III or Group V raw material is never unnecessarily supplied to the edge portion of the growth region D. As a result, difference of Group III or Group V rare material supply amount to the edge portion and central portion of the device formation region D is suppressed and the edge portion of the device region may not be convexity.