A laser beam-splitting apparatus that is capable of producing a plurality of split laser beams having a uniform laser output as well as easily and precisely adjusting the laser output of the individual split laser beams to any desired value. The apparatus is provided with one or a plurality of partial reflection and transmission mirrors each having a reflectance and transmittance which spatially and continuosly varies in one-dimensional or two-dimensional directions for the wave length of the primary laser beam. The reflectance and transmittance of each mirror for the laser beam incident thereon can be adjusted to a desired value by an adjusting device which is adapted to the position of the mirror. The laser beams reflected or transmitted from the reflection and transmission mirrors are output as the split laser beams respectively.