An image processing device includes a body that has a first connection portion and a second connection portion inside the body; an image processing board that is electrically connected to the first connection portion, the image processing board performing image processing; a functional board that is disposed so as to cover a part of the image processing board on one side of the image processing board; a side panel attached to the image processing board at a position opposite to the first connection portion, the side panel being a part of a side surface of the body; and an extension board disposed so as to cover another part of the image processing board on the same side as the functional board with respect to the image processing board, the extension board being electrically connected to the second connection portion and independently attachable to and removable from the image processing board.