An injection molding machine, comprising: an injection apparatus having a screw rotation driving section for rotating a screw inserted to a heat sleeve and a screw forward/rear move driving section for forwardly or rearwardly moving the screw at least by a hydraulic cylinder, wherein the screw has an L/D ratio between a screw length L and a screw diameter D that is set as a specific value to the injection apparatus, wherein the injection apparatus includes a cylinder attachment mechanism having a cylinder detachable section that is configured to allow the detachability of two or more different types of hydraulic cylinders (6a-c), the two or more different types of hydraulic cylinders (6a-c) comprising hydraulic cylinders (6a-c) having different dimensions to one another, each of the hydraulic cylinders (6a-c) being adaptable to a molded piece that can be molded by the screw, wherein the cylinder attachment mechanism includes a fixed block section having a fixed position that has a heat sleeve fixation section to support a rear end of the heat sleeve and two pairs of front detachable sections (13p, 13q), one of the pairs of front detachable sections (13p, 13q) being provided at each side of the heat sleeve fixation section to provide the detachability of the hydraulic cylinders (6a-c), respectively, and wherein the cylinder attachment mechanism includes the screw rotation driving section that is provided at the rear side of the fixed block section and that provides the rotation of the rear end of the screw inserted to the heat sleeve and a support block section having two pairs of rear detachable sections (15p, 15q), one of the pairs of rear detachable sections (15p, 15q) being provided at each side of this screw rotation driving section and that constitute the cylinder detachable section providing the detachability of the tip ends of the piston rods (6ar-cr) protruding from the respective hydraulic cylinders (6a-c), respectively. wherein the injection apparatus includes a cylinder attachment mechanism having a cylinder detachable section that is configured to allow the detachability of two or more different types of hydraulic cylinders (6a-c), the two or more different types of hydraulic cylinders (6a-c) comprising hydraulic cylinders (6a-c) having different dimensions to one another, each of the hydraulic cylinders (6a-c) being adaptable to a molded piece that can be molded by the screw, wherein the cylinder attachment mechanism includes a fixed block section having a fixed position that has a heat sleeve fixation section to support a rear end of the heat sleeve and two pairs of front detachable sections (13p, 13q), one of the pairs of front detachable sections (13p, 13q) being provided at each side of the heat sleeve fixation section to provide the detachability of the hydraulic cylinders (6a-c), respectively, and wherein the cylinder attachment mechanism includes the screw rotation driving section that is provided at the rear side of the fixed block section and that provides the rotation of the rear end of the screw inserted to the heat sleeve and a support block section having two pairs of rear detachable sections (15p, 15q), one of the pairs of rear detachable sections (15p, 15q) being provided at each side of this screw rotation driving section and that constitute the cylinder detachable section providing the detachability of the tip ends of the piston rods (6ar-cr) protruding from the respective hydraulic cylinders (6a-c), respectively.