To enhance the symmetricalness of the outside and inside shapes, to prevent the occurrence of unnecessary parasitic oscillation, to reduce the adhesion of a contaminant and to enhance reliability with respect to damage.

A slope 21 is formed to the outer peripheral part of a quartz plate 2 so as to become thin toward the outside by applying dry bevelling processing to the quartz plate 2 subjected to lapping processing so as to become uniform in predetermined thickness and mirror surface processing is applied to the surface and back of the quartz plate 2 containing a part (slope 21) subjected to dry processing after the dry bevelling processing by wet bevelling processing and an exciting electrode 3 is provided to the central part of the quartz plate 2.

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