Construction is achieved of a cam device that is able to effectively prevent a drive-side cam from rotating relative to a driven-side cam in a locked state. Tip-end butt sections 63 are provided on the outer-diameter side portions of tip-end surfaces 41a (40a) of convex sections of one of drive-side convex sections 34a of the drive-side cam surface 31a and driven-side convex sections 36a of the driven-side cam surface 32a, and tip-end concave sections 64 that are further recessed in the axial direction than the tip-end butt sections 63 are provided on the inner-diameter side portions of the one convex sections. In the locked state, only the tip-end butt sections 63 come in contact with the tip-end surfaces 40a (41a) of the other convex sections of the drive-side convex sections 34a and the driven-side convex section 36a.