A shaft body has an engagement portion with a slip-off preventing groove,
and a positioning recess extending from the engagement portion. A shaft
joint having an engagement groove to be engaged with the engagement
portion and a bore facing the engagement groove is provided with a
flexible member which is provided on an outer side in a longitudinal
direction of the engagement groove to be engaged with the positioning
recess. When an insufficient amount of engagement prevents engagement in
the correct position, the engagement portion contacts with the flexible
member and prevents the shaft body from engaging with the shaft joint.
When canceling the coupling for maintenance, etc., the engagement of the
flexible member with the positioning recess is cancelled by deflecting
the flexible member in a width direction of the engagement groove.
Consequently, the shaft body can be easily pulled out in a longitudinal
direction of the engagement groove.