To provide a coupling device and an image forming device using the same, simplifying the shape of projections, being easily manufactured, easily aligning centers of the rotation of a driving shaft and a driven shaft, and being easily adjusted.

The driven shaft 116 is provided with three projections 128 radially extended from the center of rotation. The driving shaft 114 is provided with projecting parts 130 on its peripheral edge at approximately equal intervals in the circumferential direction. The projecting parts 130 respectively have engagement faces 132 inclined toward the center of rotation O, and the projections 128 are partially engaged with the engagement faces 132, and are brought into contact with the engagement faces 132 when the driving shaft 114 is rotated clockwise shown in the figure. Here, as the engagement faces 132 are inclined by an angle θ toward the center of rotation O, the contact parts of the projections 128 receive the component force from the driving shaft 114 toward the center of rotation O, and the centers of rotation of the driving shaft 114 and the driven shaft 116 are aligned.