To suppress oscillation frequency fluctuation caused by fluctuation in the stray capacitance a substrate part by providing an opening at the substrate part corresponding to a gap between the input and output electrodes of a crystal, oscillator.

A crystal oscillator 2 and a control element 3 are mounted on a substrate 1. Input and output electrodes 4 at both the terminals of the crystal oscillator 2 are soldered and electrically connected to a pattern 5 on the substrate 1, and an electrode 6 of the control element 3 is soldered and electrically connected as well. At the section of the substrate 1 corresponding to the gap between the input and output electrodes 4 of the crystal oscillator 2, the opening is formed by providing a groove 7 from the left end of the substrate 1. Thus, moisture or the like is absorbed and the oscillation frequency fluctuation caused by the change in the stray capacitance between the input and output electrodes 4 of the crystal oscillator can be suppressed. When the groove 7 is further extended to right to reach the lower face of the control element 3, a temperature detecting element can detect the temperature through this groove and accuracy can be further improved.