1. A piezoelectric vibrating piece, comprising:a piezoelectric substrate, formed into a flat plate shape and vibrated in a thickness-shear vibration mode;
a first excitation electrode, formed on one principal surface of the piezoelectric substrate; and
a second excitation electrode, formed on another principal surface of the piezoelectric substrate, wherein
the first excitation electrode is formed to entirely have an identical thickness,
the second excitation electrode has a main thickness portion and an inclined portion, the main thickness portion being formed to have a constant thickness, the inclined portion being formed in a peripheral area of the main thickness portion, the inclined portion gradually decreasing in thickness from a portion in contact with the main thickness portion to an outermost periphery of the second excitation electrode, and
the main thickness portion has a thickness larger than a thickness of the first excitation electrode,
wherein the inclined portion has an inclination width as a width of the inclined portion,
the inclination width being formed to have a length of 0.5 times or more and three times or less a flexural wavelength that is a wavelength of a flexure vibration as an unnecessary vibration.