A retaining apparatus for at least one data storage device includes a tray and a retaining device. The tray is used for receiving the at least one data storage device. The retaining device includes base member, an arm member, and a retaining member. The base member is attached to the tray. The arm member is pivotably attached to the base member about a pivot axis. The pivot axis is located at a first end of the arm member. The retaining member is movably attached to the base member along a first direction. The retaining member includes an engaging portion and a retaining portion. The arm member has a driving portion at the first end engaged with the engaging portion. The first direction is substantially perpendicular to the pivot axis. The retaining member is capable of being driven to move along the first direction by rotating the arm member.