To provide a method for relatively easily producing a mold used for molding a well device having a large number of minute wells.

The method for producing the mold for molding a well plate having a plurality of aligned polygonal pillar-shaped projections includes the process (i) for forming a plurality of grooves A arranged in parallel to each other in relation to the surface of a mold substrate, the process (ii) for forming a plurality of grooves B arranged in parallel to each other on the surface of the mold substrate to cross the grooves A, and the process (iii) for forming a plurality of grooves C arranged in parallel to each other on the surface of the mold substrate to cross the grooves A and the grooves B.