There is provided a laser diode capable of setting a mesa diameter small without use of a method which loses reliability of a device, and is not easily controlled. The laser diode includes: a columnar mesa including a first multilayer film reflecting mirror, an active layer, and a second multilayer film reflecting mirror in this order, including an oxide confined layer having an unoxidized region in middle of a plane, and having a cross-sectional shape in a plane direction different from a cross-sectional shape of the unoxidized region in a plane direction; and a plurality of metal electrodes formed in regions on a top face of the mesa not facing the unoxidized region.