A resonator includes a base portion and a vibration arm. The vibration arm has first and second main faces opposite each other, the main faces have first and second grooves, the first groove has a plurality of first groove portions which are divided in the longitudinal direction of the vibration arm and arranged to be alternately shifted on both sides with respect to the longitudinal center line of the vibration arm, the second groove has a plurality of second groove portions arranged similar to the first groove portions on an opposite side to the first groove portions with respect to the longitudinal center line. A voltage is applied to excitation electrodes provided at the first and second grooves and second excitation electrodes provided on both side faces of the vibration arm, such that the vibration arm flexural-vibrates in the in-plane direction of the first or second main face.