A connecting structure is provided for connecting a first member and a second member, wherein the first member comprises a connecting upright portion and a plurality of locking flanges provided to extend outwards along the circumferential direction of the outer face of the connecting upright portion, while the second member comprises a connecting side-wall portion that overlies the connecting upright portion and a plurality of locking projections provided to extend inwards from the inner face of the connecting side-wall portion. The bottom faces of the locking flanges distend downwards in a convex curved shape and, when the second member is overlaid on the first member and rotated, the upper faces of the locking projections are guided with sliding contact along the convex curved bottom faces of the locking flanges and stopped at the lowermost position of the convex curved bottom faces.