PURPOSE: To enable a retaining wall to be constructed by a simple operation in a short time and to be made firm.

CONSTITUTION: A lock 1 for use as a retaining wall is formed into an approximately U-shaped cross section from a retaining surface wall 3, inclined approximately along a slope of the natural ground or the like and having drain holes 2, and from stacking walls 4 that extend in the direction of the slope from the upper and lower ends of the retaining surface wall 3, each of the stacking walls 4 having an engaging projection 5 or recess 6 provided therein. The lower stacking walls 4 extend more than the upper ones 4 and each comprise an opening 7 of approximately U-shaped cross section into which earth and sand can be cast and an anchor portion 8. A retaining wall is constructed in a short time by a simple operation of stacking a plurality of blocks 1 by use of the engaging projections 5 and the engaging recesses 6 of the stacking walls 4. The retaining wall A comprising the stack of blocks 1 is firmly held in place by the openings 7 through which earth and sand are cast and by the anchor portions 8 of the lower, long stacking walls 4.