A piezoelectric resonator for an oscillator contained in an upper concave portion of an insulating case that has a metal lid with which the upper concave portion is air-tightly closed comprises a GND electrode being conductively coupled to an earth pattern of the piezoelectric resonator and provided on an outer bottom face of the insulating case, a piezoelectric connecting electrode being conductively coupled to an excite electrode of the piezoelectric resonator and provided on the outer bottom face of the insulating case, and an adjustment electrode being conductively coupled to the metal lid and provided on the outer bottom face of the insulating case in such a way that a regulator circuit in an IC part conductively contacts with the adjustment electrode if the IC part including the oscillation circuit is attached to the outer bottom face of the insulating case, wherein the metal lid serves as an adjustment terminal.