A resonator element includes a quartz crystal substrate having a base, a pair of vibration arms extending from the base, and a support arm located between the vibration arms and extending from the base in the direction in which the vibration arms extend. Each of the vibration arms has an arm portion and a hammer head provided at the front end of the arm portion. The arm portion has a pair of principal surfaces and a groove that has a bottom and opens through each of the principal surfaces. In the invention, the width of each of bank-shaped portions of each of the principal surfaces that are disposed side by side on opposite sides of the groove along the width direction of the vibration arm perpendicular to the longitudinal direction thereof is set at 6 μm or smaller.