An attachment and detachment mechanism includes convex and concave engaging portions provided in first and second couplings respectively and extending in a radial direction of first and second shaft portions, the convex engaging portion is to be slidably inserted into and removed from the concave engaging portion along a longitudinal direction of the concave engaging portion, the convex and concave engaging portions includes basic positions where the longitudinal directions of the convex and concave engaging portions correspond to the attachment and detachment direction of the first and second main body portions and the convex and concave engaging portions are insertable into and removable from each other, and the attachment and detachment mechanism further includes a guide mechanism to guide one engaging portion such that the one engaging portion is disposed at the basic position in conjunction with the attachment or detachment of the first and second main body portions.
