The present invention relates to a grass-cutting apparatus in which a cutter blade is prevented from being displaced or broken when the grass-cutting apparatus collides against a solid object such as a stone or the root of a tree during grass cutting. The grass-cutting apparatus comprises: a diamond-shaped rotating disk which receives power from a main body of the apparatus in order to rotate; a grass cutter blade which is connected horizontally to the rotating disk, and which rotates in the horizontal direction by means of the rotating force of the rotating disk so as to cut grass; and a bracket which interconnects the rotating disk and the grass cutter blade.