Flow amount measurement apparatus and wireless device for use in flow amount measurement apparatus

A small-sized flow amount measurement apparatus or the like which suppresses harmonics over the conventional level. The flow amount measurement apparatus includes: a housing configured to accommodate a sensor for detecting a flow amount of a substance for measurement; a radiation conductor electrically connected to a feeding circuit on a first circuit board to radiate a high-frequency signal as a radio wave; an electrically conducting member electrically connected to the feeding circuit; and a high-frequency isolation circuit being interposed between the feeding circuit and the electrically conducting member and electrically isolating the feeding circuit from the electrically conducting member with respect to the high-frequency signal.