A gear system for combining inputs is provided. The gear system can includes: a first power source that generates a rotational force; a second power source that generates a rotational force identical to or different from the rotational force of the first power source; a third power source that generates a rotational force identical or different from the rotational forces of the first power source and the second power source; and a gear unit that generates a resultant output by combining the rotational forces from the first power source to the third power source, in which the gear unit generates a resultant output by combining torque of any two of the first power source to the third power source and combining a speed of the other power source. According to this configuration, it is possible to generate various outputs from various power sources having the same or different characteristics.