To provide a piezoelectric sensor in which a first electrode for measurement and a second electrode for reference are provided apart from each other on one surface side of a piezoelectric piece and a common electrode is provided on an opposite surface side so as to face the first and second electrodes. A piezoelectric sensor includes: a first electrode for measurement and a second electrode for reference provided apart from each other on one surface side of a piezoelectric piece; a common electrode provided on an opposite surface side of the piezoelectric piece commonly for the first electrode and the second electrode to face the first electrode and the second electrode; and an adsorption layer formed on an area, of the common electrode, to which the first electrode is faced across the piezoelectric piece, to adsorb a substance to be sensed.