A facsimile, a method of controlling the same, and an image forming apparatus having a facsimile function are provided. The facsimile includes a line terminal provided for connection with a line cord and connected with a first signal line, an external device terminal provided for connection with an external device and connected with a second signal line, a switching unit to perform switching between the first signal line and the second signal line, and a controller to determine a connection state between the line terminal and the line cord and a connection state between the external device terminal and the external device, and to, when the external device and the line cord are reversely connected respectively to the line terminal and the external device terminal, control the switching unit to interchange a path of the first signal line and a path of the second signal line.