Abstract: The computer monitor of the invention is divided into the Composite Signal Mode and the Transistor-Transistor Logic Signal Mode types depending on the computer circuit design. The compatible monitor is comprised of a composite monitor circuit adapted to the Composite Signal Mode and a transistor-transistor logic monitor circuit adapted to the Transistor-Transistor Logic Signal Mode. It includes circuits for correcting the electrical characteristics to operate on both the composite and transistor-transistor logic computer time charts. Those circuits include a horizontal shaft circuit which is connected to the horizontal oscillation/drive circuit, a vertical shift circuit is connected to the vertical oscillation/output circuit and a flyback transformer circuit. The invention also includes a circuit selecting switch integrated with a plurality of switches for freely selecting one of the computer output signals by manual switching in accordance with the mode of the computer output signal.