To absorb rain water from a joint space and to permit the water to be absorbed to the ground or a given place by embedding a material to be molded in a given size in a base material of a plastic material, pouring the material for a base form from a front surface side, curing the material, then releasing and inverting the form, filling a molding material for a surface material of a water permeable block in a recess of the base form, curing it ad then releasing it from the form.

A base outer form D with a bottom as needed and having an open upper surface and a high sidewall is disposed, and base forms 33 having suitable number of recesses 13 are laid on the bottom while forming joints 62 on its upper surface. An inner form G having a substrate middle form F of a bulky block fixed and coincident in a shape size with a form E for a molding having holes 14 corresponding partly or entirely to the recesses 13 of the forms 33 in lateral and longitudinal sizes of spaces of the substrate is provided above the forms 33. Flowable materials are filled in the recesses 13 between the forms D and G, holes 14 and a substrate space 15, the form G is removed, and the block is released from the form D. Thus, rain water is fed from joint space and absorbed to the ground or fed to a given place.