Crystal unit

A crystal unit, comprising:

• an AT-cut crystal element that has a nearly-rectangular shape in a plan view and a part as a thick portion,
• wherein
• the AT-cut crystal element includes a first end portion, a first depressed portion, the thick portion, a second depressed portion, and a second end portion in this order from a side of one short side, in viewing a cross section taken along a longitudinal direction near a center of the short side of the AT-cut crystal element,
• the first depressed portion is a depressed portion disposed from the thick portion toward a side of the first end portion, and a surface of the first depressed portion is depressed with a predetermined angle θa and subsequently bulged, and connected to the first end portion,
• the second depressed portion is a depressed portion disposed from the thick portion toward a side of the second end portion, and a surface of the second depressed portion is depressed with a predetermined angle θb and subsequently bulged, and connected to the second end portion, and
• when a dimension from a distal end of the first end portion to an edge on a side of the second depressed portion of the thick portion is defined as L, the L satisfies a following formula (1),
• in the formula (1), n is a natural number, and λ is a wavelength of a flexure vibration that propagates along an X-axis of a crystal in the crystal unit,
• L=λ×(n/2±⅛) (1).