In a quartz crystal unit, the unit comprising a case, a quartz crystal tuning fork resonator and a lid, the resonator having a tuning fork base, and first and second tuning fork tines, each of the first and second tuning fork tines having a first side surface and a second side surface opposite the first side surface, the first side surface of the first tuning fork tine confronting the second side surface of the second tuning fork tine; at least one groove having a plurality of surfaces including a first surface being formed in at least one of first and second main surfaces of each of the first and second tuning fork tines so that only the first surface of the at least one groove is directly opposite the first side surface of the corresponding tuning fork tine and a width of the at least one groove is greater than or equal to a distance in the width direction of the at least one groove measured from an outer edge of the at least one groove to an outer edge of the corresponding one of the first and second tuning fork tines and less than 0.07 mm.