To provide an electronic circuit design support system for automatically extracting the circuit information before and after a change per each net to output the extracted differential circuit information.

This electronic circuit design support system is formed of memory means 105 and 106 for storing the first circuit information before a change and the second circuit information after the change of a circuit, in which net name is given to the information such as the electronic circuit connecting condition, a circuit mark of electronic parts and pin number, a control device 101 for reading the first circuit information and the second circuit information from the memory means 105 and 106 and for comparing them with each other to extract a difference between them as a differential circuit information, and an input/output device 103 for outputting the differential circuit information extracted by the control device 101. With this structure, the work for confirming property of a change part is eliminated, and even if the number of net and quantity of the information to be given to the net are suddenly increased, a human error such as a confirmation omission and wrong confirmation in the confirmation work can be eliminated.