DEVICE DIAGNOSIS SYSTEM THAT DECIDES WHETHER OPERATING SOUND OF IMAGE FORMING APPARATUS, COLLECTED BY PORTABLE TERMINAL DEVICE, CONTAINS ABNORMAL NOISE, AND DEVICE DIAGNOSIS METHOD

A device diagnosis system includes an image forming apparatus, a portable terminal device, and an abnormal noise decision device. The portable terminal device collects an operating sound of the image forming apparatus, at a sound collecting position selected from a plurality of predetermined sound collecting positions relative to the image forming apparatus. The abnormal noise decision device (a) identifies a decision criterion corresponding to the sound collecting position, and (b) decides whether the operating sound contains an abnormal noise, on a basis of acoustic data of the operating sound collected, in accordance with the decision criterion identified.