A manufacturing method for a large-scale diamond substrate and the produced substrate that is suitable for semiconductor lithography processing and large-scale optical parts, semiconductor materials, thermal-release substrate, semiconductor wafer processing, back-feed devices, and others. The manufacturing method of the present invention includes: preparing a substrate having a main face including a first region which is a concave and a second region which surrounds the first region, and mounting, on the first region, a single crystalline diamond seed substrate having a plate thickness thicker than the concave depth of the first region; forming a CVD diamond layer from the single crystalline diamond seed substrate using a chemical vapor deposition, and mutually connecting by forming a CVD diamond layer on the second region at the same time; and polishing to substantially flatten both the CVD diamond layers and on the second region by mechanically polishing.