A piezoelectric oscillator includes a piezoelectric vibrating piece, an integrated circuit, and a package. The package includes a first layer, a second layer, a third layer, and a fourth layer. The ceiling surface as a portion of the inferior surface of the third layer has a rectangular shape surrounded by short sides and long sides. The ceiling surface includes a pair of frequency checking terminals electrically connected to the connecting electrodes and control terminals to control the integrated circuit. The pair of the frequency checking terminal are adjacent to one another. The respective frequency checking terminals are disposed in contact with any of the long sides and one of the short sides. The control terminals are extracted to the top surface of the third layer, and overlap the frequency checking terminals in a vertical direction on the top surface of the third layer to be connected to the mounting terminals.