A technique related to a substrate manufacturing method is provided. The substrate manufacturing method comprises irradiating laser into an ingot of gallium nitride (GaN) along a direction substantially vertical to a surface of the ingot and forming a reformed layer in which gallium has precipitated and that is substantially parallel to the ingot surface. The substrate manufacturing method comprises separating the ingot into a plurality with a position where the reformed layer has been formed as a boundary by dissolving the reformed layer.