A holding frame includes a base plate, a first resisting wall, a second resisting wall, two first elastic arms and two second elastic arms. The base plate includes a first surface and a second surface opposite to the first surface. The first resisting wall extends from the first surface, and the second resisting wall extends from the second surface. The two first elastic arms are formed on the first surface, and face the first resisting wall. The two first elastic arms and the first resisting wall define a first receiving space configured for receiving a first hard disk drive. The two second elastic arms are formed on the second surface, and face the second resisting wall. The two second elastic arms and the second resisting wall define a second receiving space configured for receiving a second hard disk drive.