A dishwasher having a tub having a front defining an outer periphery, a treating chamber defined by the tub and having an open face located at the front of the tub and within the outer periphery, and a cover selectively closing the open face. The two optical waveguides are arranged such that they respectively receive a measurement light portion of the measurement light and that the measurement light portions are superimposed after passing through the optical waveguides. The terminal device preferentially connects to the relay device having the best communication quality based on each of the communication quality information.