A flexural vibration piece includes a base, and a vibrating arms extending therefrom, each pair of vibrating arms has a first groove formed in the extension direction of the vibrating arm in one main surface following the direction in which the pair of vibrating arms are aligned, and a second groove formed side by side to the first groove in another main surface, the sum of the depths of the first and second groove portions is greater than the interval between the one main surface and the other main surface, and a mass portion is provided on each of the pair of vibrating arms, on the one main surface which is the opening side of the first grooves formed toward the outer sides opposite the inner sides on which the vibrating arms face each other.