A medium storage apparatus for an automated teller machine, comprising: a main body that forms an overall external appearance of the automated teller machine and serves as a base for installing or embedding other components of the automatic teller machine; a body cover installed at the main body having one side and at least one side surface; a medium storage box attached to or detached from is the one side of the body cover while sliding into and out of the body cover and configured to store a medium in an inner space of the medium storage box; a side door provided on at least one of both side surfaces of the medium storage box and configured to open and close the inner space of the medium storage box; and a hinge portion configured to pivotably connect the side door to the medium storage box, wherein an opening is formed on the at least one side surface of the body cover, and the side door is disposed to face the opening in a state where the medium storage box is attached to the body cover, wherein, when the medium storage box is slidably attached to or detached from the one side of the body cover, the whole of the medium storage box is accommodated in the body cover, wherein, when the side door is opened in a state where the medium storage box is attached to the body cover, the side door is pivoted to project to an outside of the body cover through the opening, such that the medium stored in the medium storage box can be taken out to the outside of the body cover through the opening, and wherein the body cover is hinge-pivoted from the main body to secure enough space for allowing access to the medium storage box at the time of attaching or detaching the medium storage box to or from the body cover. a main body that forms an overall external appearance of the automated teller machine and serves as a base for installing or embedding other components of the automatic teller machine; a body cover installed at the main body having one side and at least one side surface; a medium storage box attached to or detached from is the one side of the body cover while sliding into and out of the body cover and configured to store a medium in an inner space of the medium storage box; a side door provided on at least one of both side surfaces of the medium storage box and configured to open and close the inner space of the medium storage box; and a hinge portion configured to pivotably connect the side door to the medium storage box, wherein an opening is formed on the at least one side surface of the body cover, and the side door is disposed to face the opening in a state where the medium storage box is attached to the body cover, wherein, when the medium storage box is slidably attached to or detached from the one side of the body cover, the whole of the medium storage box is accommodated in the body cover, wherein, when the side door is opened in a state where the medium storage box is attached to the body cover, the side door is pivoted to project to an outside of the body cover through the opening, such that the medium stored in the medium storage box can be taken out to the outside of the body cover through the opening, and wherein the body cover is hinge-pivoted from the main body to secure enough space for allowing access to the medium storage box at the time of attaching or detaching the medium storage box to or from the body cover.