A piezoelectric resonator element includes a piezoelectric substrate formed of an AT-cut quartz crystal substrate in which the thickness direction thereof is a direction parallel to the Y′ axis; and excitation electrodes disposed so as to face vibrating regions on both front and rear principal surfaces of the piezoelectric substrate. The piezoelectric substrate includes a rectangular excitation portion in which sides parallel to the X axis are long sides thereof, and sides parallel to the Z′ axis are short sides thereof; and a peripheral portion having a smaller thickness than the excitation portion and formed around the excitation portion. Each of side surfaces of the excitation portion extending in a direction parallel to the X axis is present in one plane, and each of side surfaces of the excitation portion extending in a direction parallel to the Z′ axis has a step.