In the oscillator, a quartz crystal resonator and an oscillation circuit formed in an IC incorporating an inductor are electrically coupled to each other with a resonator interconnection disposed on a surface of a substrate to form an oscillation loop. A conductor layer disposed as an intermediate layer of the substrate is disposed so as to overlap the resonator interconnection and not to overlap the inductor incorporated in the IC in a plan view.

In the oscillator, a quartz crystal resonator and an oscillation circuit formed in an IC incorporating an inductor are electrically coupled to each other with a resonator interconnection disposed on a surface of a substrate to form an oscillation loop. A conductor layer disposed as an intermediate layer of the substrate is disposed so as to overlap the resonator interconnection and not to overlap the inductor incorporated in the IC in a plan view.

A wiring pattern for oscillation input signal and a wiring pattern for oscillation output signal are provided on a printed circuit board, and a wiring pattern for ground power source voltage is arranged in a region therebetween. A quartz crystal unit is connected between the wiring pattern for oscillation input signal and the wiring pattern for oscillation output signal and one ends of capacitors serving as load capacitors thereof are connected to the wiring pattern for ground power source voltage. Further, a wiring pattern for VSS is arranged so as to enclose these wiring patterns, and a wiring pattern for VSS is arranged also in a lower layer in addition thereto. By this means, reduction of a parasitic capacitance between an XIN node and an XOUT node, improvement in noise tolerance of these nodes and others can be achieved.