Patent ID: 8229324

Claim:
A coupling device that couples a driven shaft and a drive shaft in a situation where a processing unit that can be detachably installed in an apparatus body is positioned with respect to the apparatus body, the drive shaft configured to be coupled to a drive source provided in the apparatus body, the driven shaft configured to be coupled to a rotating body provided in the processing unit, the rotating body being at least one of a developing roller, a drive roller of an intermediate image transfer belt, a drive roller of a paper conveying belt, a roller that conveys paper, and a secondary image transfer roller, the coupling device comprising: two constant velocity joints arranged in series in a shaft direction, the constant velocity joint including, a ball non-retaining member that has an annular space with one opened end, the ball non-retaining member having a plurality of track grooves extending in the shaft direction of the ball non-retaining member on an external wall surface or an inner wall surface of the annular space at a constant interval in a circumferential direction, and a ball retaining member having a portion that engages with the annular space of the ball non-retaining member, and that retains a ball that slides along each of the track grooves formed in the ball non-retaining member, wherein either one of the constant velocity joints interlocks with attachment and detachment of the processing unit in the apparatus body to engage and separate the ball non-retaining member and the ball retaining member with and from each other.