We construct an infinite family of slice disks with equivalent exteriors, which gives an affirmative answer to an old question asked by Hitt and Sumners in 1981. Furthermore, we prove that these slice disks are ribbon disks. Recently, Akbulut constructed a pair of non-isotopic equivalent ribbon disks using the Mazur cork. We discuss this pair of ribbon disks. This is a joint work with Motoo Tange.