An object is to provide a frequency adjustment method for a piezoelectric resonator device that is applicable to a microminiaturized device and that can adjust the frequency without deteriorating the accuracy of frequency adjustment. A frequency adjustment method for a tuning-fork quartz resonator is applicable to a tuning-fork quartz resonator that includes a tuning-fork quartz resonator piece having a pair of resonator arms 31, 32 and metallic adjustment films W formed on the resonator arms. The frequency adjustment method adjusts the frequency by reduction of a mass of the metallic adjustment films W. The frequency adjustment method includes: a rough adjustment step for roughly adjusting the frequency by partially thinning or removing the metallic adjustment films W; and a fine adjustment step for finely adjusting the frequency by at least partially thinning or removing products W1, W2 derived from the metallic adjustment film W during the rough adjustment step.