A sealed worm gear type finger joint unit for a robot hand has a circular opening in a gear box case of the unit, and the opening is closed by a rubber bush. When the rubber bush is removed, a shaft end face of a worm shaft section is exposed from the circular opening, and this makes a tool engagement section formed on the shaft end face is accessible from the outside. A tool for turning the worm shaft section is fitted in the tool engagement section, and the worm shaft section can be easily turned by the tool. Turning the worm shaft section turns a worm, turning a worm wheel meshing with the worm, and this turns the joint shaft. As a result, a swing arm connected to shaft end sections of the joint shaft can be moved to a predetermined position. In the finger joint unit, the joint shaft can be easily manually turned.