There is provide a manufacturing method of a fin-integrated substrate capable of producing by simple process a fin-integrated substrate with heat radiating fins at fine pitches by a processing method in which warpage of a metal base plate and corrugation (wavy shape) of the heat radiating fins are suppressed. There is provided a manufacturing method of a fin-integrated substrate in which bonding of the metal circuit board to the ceramic substrate is performed by a molten metal bonding method, and formation of the plurality of heat radiating fins at a cut part that is a part of the metal base plate is performed by fixing 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.