To provide a form for manufacturing a block which can rapidly and inexpensively deal with various requests regarding change of block shape.

The bottom plate corresponding component in the form for manufacturing the block for building a water channel has a base 1, and a surface plate detachably arranged on the base 1. The form comprises a mechanism for vertically moving a plurality of inserts 15 for forming a drain port CB1f in the block CB1 in the base 1. The form selectively uses the surface plate (3) having insert inserting holes 3a1, 3b1 or the surface plate (20) capable of forming an opening for mounting a grating, thereby manufacturing the block CB1 having the plurality of the drain ports CB1f on the upper surface and the block CB5 having an opening CB5f for mounting the grating.