Patent ID: 7401555

Claim:
A shaft coupling method of coupling a first shaft and a second shaft, comprising the steps of: screwing for a first distance a first screw portion of a grip unit having a grip portion and provided at a first end of the first shaft to grip the second shaft onto a second screw portion of a grip force acting unit configured to cause a grip force for gripping the second shaft to act on a grip portion by moving the grip portion in a radial direction of the first shaft; engaging the second shaft with the grip force acting unit such that the second shaft is not rotatable relatively to the grip force acting unit when the first and second screw portions have been screwed onto each other for the first distance; and screwing the first and second screw portions onto each other further for a second distance from the first distance until the first end of the first shaft and a first end of the second shaft face each other within a shaft center holding portion of the grip unit such that the grip portion does not overlap the first end of the first shaft or the first end of the second shaft, and the screwing is accomplished by rotating the second shaft and restricting rotation of the first shaft to cause the grip force acting unit to move the grip portion in the radial direction such that the grip portion grips the second shaft.