Provided are intermediate coupling unit that can maintain universal applicability of image forming apparatus so it can singly form images/be installed in small offices, but can also couple two apparatuses if necessary, and image forming apparatus adaptable to this unit. Intermediate coupling unit includes carry-in port at lower surface right side, plural conveying roller pairs sandwiching and conveying internally-carried-in recording medium, discharge ports formed near upper surface right/left ends for externally discharging recording medium, first/second flaps switching among conveying paths, A, B, C, paper discharge tray fixed at upper internal position, and internal paper feed cassette detachable downward. Two identical-shape printers are linked through conveying path A and enable double-speed-printing when coupled to top/bottom of intermediate coupling unit to face same direction, and linked through conveying path B and enable fast-double-side-printing when coupled to face opposite directions.