A metal base having plural protrusions at its bottom is engaged with and placed on standing metal pins in plural through holes provided in a base board, and a circuit board is fitted to an upper end of the metal pins. A crystal resonator is arranged on the circuit board via a heater element, and the metal base is covered with a metal cover, thereby obtaining a sealed structure of the crystal resonator. A two-stage counterbored portion including a first-stage and a second-stage counterbored portions is formed in the bottom of the base board, and a solder or conductive resin is filled in a gap between the first-stage counterbored portion formed around the metal pin inserted into the through hole, and the through hole and the metal pin to fix the metal pin in the though hole. Slits penetrating through the base board are formed around the metal pin.