To provide a forming technique wherein when a reticulated form plate is mounted to a reinforcing bar assembly, which is installed beforehand on the ground, the spacing between the form plate and the assembly can be set easily and precisely, and accurate finish width dimensions of a mold for slope protection and covering dimensions of the reinforcing bar assembly can be easily obtained.

A reinforcing bar assembly 6 formed from reinforcing bars 4 and stirrups 5 is installed at a predetermined position on the ground 2. And when reticulated form plates 7, 8 are attached to the assembly 6 from the opposite sides thereof, horizontal contact bars 11 attached to the plates 7, 8 so as to be spaced therefrom by a predetermine interval Ls are brought into contact with the stirrup 5 having precise dimensions, whereby the interval between the plates 7, 8 can be always maintained constant.