A method for manufacturing a quartz crystal unit comprises the steps of adjusting an oscillation frequency of a quartz crystal tuning fork resonator that is vibratable in a flexural mode of an inverse phrase and that has first and second quartz crystal tuning fork tines, forming at least one groove in each of two of opposite main surfaces of each of first and second quartz crystal tuning fork tines, disposing an electrode on a surface of the at least one groove formed in each of two of the opposite main surfaces and each of two of opposite side surfaces of each of the first and second quartz crystal tuning fork tines so that the electrodes of the grooves of the first quartz crystal tuning fork tine are connected to the electrodes of the side surfaces of the second quartz crystal tuning fork tine and the electrodes of the grooves of the second quartz crystal tuning fork tine are connected to the electrodes of the side surfaces of the first quartz crystal tuning fork tine, the quartz crystal tuning fork resonator having a series resistance R.sub.1 of a fundamental mode of vibration less than a series resistance R.sub.2 of a second overtone mode of vibration, mounting the quartz crystal tuning fork resonator on a mounting portion of a case, and connecting a lid to the case to cover an open end of the case.