PURPOSE: To increase the anti-leakage performance for the seal part between the plug and the case, by bonding after the provision of multi-steps at the plug and case bonding part of the airtight seal package containing crystal oscillator.

CONSTITUTION: In the cylindrical type airtight seal package containing the crystal oscillator 9, multiple-steps are provided with the plug 3 and the case 7 to bond each other with the sealing material 10. The anti-leakage performance is excellent independently of the quality of material and amount of the sealing material, and as shown in the plug 6, taper is provided, then smooth and non-eccentric sealing can be made. Thus, by providing multiple-steps to the plug or the case, it is effective sufficiently if it is used singly. The effect can further be increased by the combined use of the plug and the case with steps to avoid leakage perfectly against shock, temperature, and time aging.