A quartz crystal unit comprising a case having an interior space and a mounting portion in the interior space, and a quartz crystal resonator having a base portion and first and second vibrational arms, the quartz crystal resonator being vibratable in a flexural mode, a capacitance ratio r1 of a fundamental mode of vibration of the quartz crystal resonator being less than a capacitance ratio r2 of a second overtone mode of vibration thereof, a mounting arm protruding from the base portion and extending in a common direction with at least one of the first and second vibrational arms, the mounting arm being mounted on the mounting portion of the case, an electrode being disposed on a surface of the mounting arm and a surface in the interior space of the case, the electrode disposed on the surface of the mounting arm being connected to the electrode disposed on the surface in the interior space of the case.