A piezoelectric substrate includes vibrating arms, a base portion to which one end portion of each vibrating arm is connected, spindle portions formed in the other end portion of each vibrating arm, formed to have a large width, and having first groove portions formed therein, and second groove portions that are formed along the resonator center line of each vibrating arm, and flexure-torsional combined resonator is excited. A piezoelectric resonator element has flexural resonator of flexure-torsional combined resonator that is excited as its principal resonator and sets the cutting angle of the piezoelectric substrate, the widths and the depths of the first groove portion and the second groove portion, and the thickness of the vibrating arm such that the frequency-temperature characteristics represent third-order characteristics with respect to the temperature.