A piezoelectric oscillator is provided, which has a through electrode providing reliable conduction between a piezoelectric vibrating piece and an external electrode with rare occurrence of a large stress caused by temperature variation in processing or deformation of a mounted base substrate, while the hermeticity of a cavity is maintained. A piezoelectric oscillator having a piezoelectric vibrating piece sealed in a cavity defined between a base substrate and a lid substrate includes a through electrode disposed in a through hole penetrating through the base substrate, and the through electrode has a glass frit filled in the through hole and fired and a core formed of a material containing only iron and nickel and disposed in the through hole together with the glass frit. The values of the thermal expansion coefficients of the base substrate, the glass frit, and the core are set as: base substrate glass≧frit>core.