An engaging mechanism includes an engaging member and an engaged member freely detachably engageable with the engaging member. The engaging member includes an engaging main part and an engaging claw part formed on the engaging main part, both resiliently deformable. The engaging claw part has an inwardly curved engaging surface defined by a first curvature continuous curve. The engaged member includes an engaged part engageable with the engaging claw part and having an outwardly curved engaged surface defined by a second curvature continuous curve. The engaging surface and the engaged surface contact each other at a linear contact area at a time from when the engaging claw part and the engaged part are in engagement with each other through to when the engaging claw part is disengaged from the engaged part. A curvature of the engaging surface at the linear contact area is smaller than a curvature of the engaged surface at the linear contact area.