A retaining device includes a computer cage (30), a drive bracket (20) for receiving a storage device, a displacing assembly (40) movably combining the drive bracket and the computer cage together. The displacing assembly includes a first fixing member (42) slidably attached to the bottom of the drive bracket, a second fixing member (44) secured in the computer cage, and a pair of connecting members (46) pivotably disposed between the first fixing member and the second fixing member. The connecting member comprises a first post (462), and a second post (464) parallel to the first post. The first and second fixing member each define a corresponding semicircular slot (424,442) to engagingly receiving the posts. The drive bracket is moved in and out form the computer cage, with the first and second posts of the connecting member pivotally engaging in the semicircular slots of the first and the second fixing member.