In an exemplary embodiment, a vibration waveform sensor includes a pair of conductive pads 22, 23, and a piezoelectric element 30 whose terminal electrodes are connected thereto, which are provided on a board 20, and these are surrounded by a conductive ring-like spacer 40. On the interior side of the spacer 40, a cover part 44 substantially like a disk is provided in a manner covering over the pair of conductive pads 22, 23 and the piezoelectric element 30. The cover part 44 cuts off any humming noise from the top face of the piezoelectric element 30 over a continuous surface, which results in a reduction of humming noise.