Abstract: A method for manufacturing a laser diode using Group III nitride compound semiconductor comprising a buffer layer 2, an n+ layer 3, a cladding layer 4, an active layer 5, a p-type cladding layer 61, a contact layer 62, an SiO2 layer 9, an electrode 7 which is formed on the window formed in a portion of the SiO2 layer 9, and an electrode 8 which is formed on a portion of the n+ layer 3 by etching a portion of 4 layers from the contact layer 62 down to the cladding layer 4. One pair of opposite facets S of a cavity is formed by RIBE, and then the facets are etched by gas cluster ion beam etching using Ar gas. As a result, the facets S are flatted and the mirror reflection of the facets S is improved.