1. An AT-cut crystal element, comprising:side surfaces that intersect with a Z?-axis of a crystallographic axis of crystal,
at least one side surface of the side surfaces being constituted of three surfaces of a first surface, a second surface, and a third surface, wherein
the first surface being an m-surface of a quartz crystal,
the second surface intersecting with the first surface and being other than the m-surface,
the third surface intersecting with the second surface and being other than the m-surface.