A laser beam mixing apparatus to convert a laser beam bundle into a single laser beam having a uniform energy density. The laser beam mixing apparatus includes: a barrel to adjust a distance between a multi-core optical cable and an optical lens included therein, to convert a laser beam bundle into a single beam; and a stage to adjust the position and angle a single-core optical cable with respect to the optical lens, to align the core of the single-core optical cable with the center of the single beam.