An accessory and an accessory for an image pickup apparatus are provided and are advantageous in reducing cost by reducing the number of parts. A retaining ring is engaged in an annular groove formed in an outer circumference of a cylindrical part of a wide-angle converter lens. Each of retaining ridges has a bottom wall extending from the inner circumference of the annular part in the direction of the width of the annular part in a recess, and a protruded wall extending radially outward of the annular part from the end of the bottom wall, spaced from the annular part, and protruding radially outward from the first outer circumference. When the parts, provided with the retaining ridges, of the annular part are depressed radially inward of the annular part, the protruded wall sink radially inward from the first outer circumference.