An input synthesis apparatus according to the present invention includes: a first input unit which provides first rotational force; a second input unit which provides second rotational force equal to or different from the first rotational force; a gear unit which is engaged with the first input unit and the second input unit and synthesizes the first rotational force and the second rotational force; and an output unit which outputs resultant force of the first rotational force and the second rotational force, in which the gear unit sums up speeds or torque of the first rotational force and the second rotational force based on whether a rotation direction of the first input unit and a rotation direction of the second input unit are identical to each other.