To eliminate such a risk that a grass cutter blade hits a support during the cutting work of grass, by laying a pair of protective blocks against the support at the ground surface of the lower outer peripheral face of the support.

The peripheral ground of a support g2 is excavated to secure an installation space S where a pair of protective blocks 1, 1 for the support can be laid. Then, the butting face of a pair of protective blocks 1, 1 around the support g2 are met in the installation space S and both blocks 1, 1 are installed. The front fixing ends of a cramp iron 2 are inserted in the fixing hole 1e formed at the front and rear side faces of both blocks 1, 1 respectively and fixed therein. The peripheral area of both blocks is filled back with soil to expose only the upper face of both blocks. Accordingly, grasses are prevented from growing at least on the protective tool A of the support. And hence, the support g2 can be easily confirmed during the cutting work of grasses by use of a grass cutter and the grass cutter is not required to bring it close to the support.