The present invention provides a locking device having a simplified and energy saving configuration that assures to prevent an unintentional erroneous removal of a container case in operation mode from an apparatus main body. The locking device comprises: first engagement device which is an engagement hole 10 provided in an electronic apparatus main body 1; and second engagement device provided in a disc container case 2 that is inserted into and removed from the electronic apparatus through an opening 1a of the electronic apparatus main body 1. The second engagement device includes a movable engagement piece 21 constituted to be movable toward the engagement hole 10 and a movement urging mechanism 23 for urging this movable engagement piece 21. This movement urging mechanism 23 consists of a working member 23A made from a shape-memory alloy that change its distance from a first end to a second end when subjected to a heat; and a fixed base 24 for fixing the second end of the working member 23A.