A component set for a driving device including a motor unit and a speed reducer attached to the motor unit, comprising components constituting the motor unit, and components constituting the speed reducer, wherein the components constituting the motor unit including a motor with a rotational shaft, characterized in that the components constituting the speed reducer includes a plurality of transmission gears (35 to 37) meshing to decelerate an output of the motor; a plurality of different types of gear cases (30A to 30C) each configured for supporting the plurality of transmission gears (35 to 37) and selectively attachable to the motor unit, an input shaft configured to be coaxially arranged with the rotational shaft when the speed reducer is attached to the motor unit to receive a driving force of the rotational shaft, and an output shaft (34A, 34B) to output the decelerated rotation output from the motor; wherein the plurality of different types of gear cases (30A to 30C) are different from one another in an arrangement of the plurality of transmission gears (35 to 37) and a position of the output shaft (34A, 34B) relative to the input shaft, wherein the plurality of transmission gears (35 to 37) used for each of the different types of gear cases (30A to 30C) are the same, and wherein the plurality of transmission gears (35 to 37) are spur gears, the input shaft comprises an input gear and the output shaft (34A, 34B) comprises an output gear (38A, 38B) to transmit the driving force of the input shaft from the input gear through the transmission gears (35 to 37) and the output gear (38A, 38B) to the output shaft (34A, 34B), and the plurality of different types of gear cases (30A to 30C) include: a second gear case in which shafts (35c to 37c) of the plurality of transmission gears (35 to 37) are arranged in line in a radial direction of the rotational shaft or the input shaft; and a first gear case (30A, 30B) in which a plurality of transmission gears (35 to 37) among the plurality of transmission gears (35 to 37) are annularly arranged in the circumferential direction of the input shaft that means around the rotational shaft of the motor when the speed reducer is attached to the motor unit. components constituting the motor unit, and components constituting the speed reducer, wherein the components constituting the motor unit including a motor with a rotational shaft, characterized in that the components constituting the speed reducer includes a plurality of transmission gears (35 to 37) meshing to decelerate an output of the motor; a plurality of different types of gear cases (30A to 30C) each configured for supporting the plurality of transmission gears (35 to 37) and selectively attachable to the motor unit, an input shaft configured to be coaxially arranged with the rotational shaft when the speed reducer is attached to the motor unit to receive a driving force of the rotational shaft, and an output shaft (34A, 34B) to output the decelerated rotation output from the motor; a plurality of transmission gears (35 to 37) meshing to decelerate an output of the motor; a plurality of different types of gear cases (30A to 30C) each configured for supporting the plurality of transmission gears (35 to 37) and selectively attachable to the motor unit, an input shaft configured to be coaxially arranged with the rotational shaft when the speed reducer is attached to the motor unit to receive a driving force of the rotational shaft, and an output shaft (34A, 34B) to output the decelerated rotation output from the motor; wherein the plurality of different types of gear cases (30A to 30C) are different from one another in an arrangement of the plurality of transmission gears (35 to 37) and a position of the output shaft (34A, 34B) relative to the input shaft, wherein the plurality of transmission gears (35 to 37) used for each of the different types of gear cases (30A to 30C) are the same, and wherein the plurality of transmission gears (35 to 37) are spur gears, the input shaft comprises an input gear and the output shaft (34A, 34B) comprises an output gear (38A, 38B) to transmit the driving force of the input shaft from the input gear through the transmission gears (35 to 37) and the output gear (38A, 38B) to the output shaft (34A, 34B), and the plurality of different types of gear cases (30A to 30C) include: a second gear case in which shafts (35c to 37c) of the plurality of transmission gears (35 to 37) are arranged in line in a radial direction of the rotational shaft or the input shaft; and a first gear case (30A, 30B) in which a plurality of transmission gears (35 to 37) among the plurality of transmission gears (35 to 37) are annularly arranged in the circumferential direction of the input shaft that means around the rotational shaft of the motor when the speed reducer is attached to the motor unit. a second gear case in which shafts (35c to 37c) of the plurality of transmission gears (35 to 37) are arranged in line in a radial direction of the rotational shaft or the input shaft; and a first gear case (30A, 30B) in which a plurality of transmission gears (35 to 37) among the plurality of transmission gears (35 to 37) are annularly arranged in the circumferential direction of the input shaft that means around the rotational shaft of the motor when the speed reducer is attached to the motor unit.