A manufacturing method of a fin-integrated substrate, wherein a metal circuit board made of aluminum or an aluminum alloy is bonded to one surface of a ceramic substrate, one surface of a metal base plate in a flat plate shape made of aluminum or an aluminum alloy is bonded to another surface of the ceramic substrate, and a plurality of heat radiating fins are formed integrally with the metal base plate in a manner to project from another surface of the metal base plate and to be arranged at predetermined intervals from each other, wherein a heat conductivity of the metal base plate is 170 W/(m*K) or more, a hardness of the metal base plate is a Vickers hardness Hv of 20 to 40, a width of the heat radiating fin is 0.2 to 2.0 mm, a width of a groove part formed between the plurality of heat radiating fins is 0.2 to 2.0 mm, a depth of the groove part is 2 to 20 mm, and a thickness of a portion of the metal base plate where the heat radiating fin is not formed is 3.0 to 5.0 mm, wherein bonding of the metal circuit board to the ceramic substrate is performed by a molten metal bonding method, and for forming the metal base plate having the heat radiating fins integrally formed therewith, a cut material composed of a base part and a cut part is used, and formation of the plurality of heat radiating fins at the cut part is performed by fixing the cut material by a jig to apply a tensile stress on a surface of the cut part where the heat radiating fins are to be formed, and performing grooving processing of forming a plurality of grooves by moving a multi-cutter composed of a plurality of stacked disc-shaped cutters, on the surface to which the tensile stress is applied, while rotating the multi-cutter, to form the metal base plate having the heat radiating fins integrally formed therewith, and wherein the fixation of the cut material by the jig is performed by inserting the base part into the jig and fixing the cut material with the tip ends of screws. wherein a metal circuit board made of aluminum or an aluminum alloy is bonded to one surface of a ceramic substrate, one surface of a metal base plate in a flat plate shape made of aluminum or an aluminum alloy is bonded to another surface of the ceramic substrate, and a plurality of heat radiating fins are formed integrally with the metal base plate in a manner to project from another surface of the metal base plate and to be arranged at predetermined intervals from each other, wherein a heat conductivity of the metal base plate is 170 W/(m*K) or more, a hardness of the metal base plate is a Vickers hardness Hv of 20 to 40, a width of the heat radiating fin is 0.2 to 2.0 mm, a width of a groove part formed between the plurality of heat radiating fins is 0.2 to 2.0 mm, a depth of the groove part is 2 to 20 mm, and a thickness of a portion of the metal base plate where the heat radiating fin is not formed is 3.0 to 5.0 mm, wherein bonding of the metal circuit board to the ceramic substrate is performed by a molten metal bonding method, and for forming the metal base plate having the heat radiating fins integrally formed therewith, a cut material composed of a base part and a cut part is used, and formation of the plurality of heat radiating fins at the cut part is performed by fixing the cut material by a jig to apply a tensile stress on a surface of the cut part where the heat radiating fins are to be formed, and performing grooving processing of forming a plurality of grooves by moving a multi-cutter composed of a plurality of stacked disc-shaped cutters, on the surface to which the tensile stress is applied, while rotating the multi-cutter, to form the metal base plate having the heat radiating fins integrally formed therewith, and wherein the fixation of the cut material by the jig is performed by inserting the base part into the jig and fixing the cut material with the tip ends of screws.