A resonator element includes a base portion in which a pair of notches is formed, a pair of resonating arms which is extended in parallel from one end side of a first portion of the base portion. The resonating arm is provided with a bottomed elongated groove which has an opening along at least one principal surface of both principal surfaces and a weight portion which is formed at the tip end side of the resonating arm on the opposite side of a root of the resonating arm attached to the base portion and which has a larger width than on the root side. The weight portion is formed so that the proportion of the length of the weight portion to the length from the root to the tip end side in a longitudinal direction of the resonating arm is within a range of 35% to 41%.