PURPOSE: To enhance working efficiency of patch processing method for the input/output terminal of an online scope by providing the patch processing method with the function that if the type of input/output terminal of a target to be connected to a line is other than expected one, the method is provided with a patch box function available for switching the type of an input/output signal at the input/output terminal to the type of the input/output terminal to be able to correct the input/output signal automatically.

CONSTITUTION: Online scope 7 has the function of switching the type of input/ output terminal that executes the function of patch box 2 by means of software, and is connected to the target 3 via a signal line cable 5. Even if input/output terminal of target 3 is different in type from the input/output of a relevant online scope 7, with the aid of control signal one out of two state buffer circuits 8 and 9 can be set into a floating state and the type of an input/output signal can be automatically corrected. Further, if the type of the input/output terminal of target 3 is known in advance, by storing the content of a set type in a memory, the content of the type of the input/output terminal can be easily changed even when target 3 is changed.