Provided is a pipeline network diagnosing device in which: a pressure measurement value is stored upon being acquired by a pressure gauge; a pipeline network is divided into sub-networks at the installation positions of an air compressor, a terminal device, and a pressure gauge installed partway along a pipeline channel, after which a sub-network model is generated; the flow of air within a sharing sub-network configured from two sub-networks that share the pressure gauge is calculated and stored, the pressure measurement value at an end part of the sharing sub-network serving as a calculation criterion; the pressure measurement value and a pressure calculation value at a shared pressure measurement point are compared to each other, the shared pressure measurement point being a pressure measurement point shared by the two sub-networks within the sharing sub-network; an assessment is made for each of the sub-networks with regard to whether air has leaked or a device has clogged; and any sub-networks in which air leakage or device clogging is assessed to have occurred are displayed on a display device using the results of the aforementioned assessment.