A piezoelectric device comprising: a piezoelectric vibration piece having an outer shape rectangular in plan view and provided with driving electrodes (9,10) on front and back main surfaces thereof, the piezoelectric vibration piece further including a pair of electrodes (11,12) for respectively extracting the driving electrodes (9,10) toward one of a first pair of opposing sides of two pairs of opposing sides forming the rectangular shape; a base member having two electrode pads (7,8) on an upper surface thereof, the electrode pads (7,8) being respectively connected to the pair of electrodes (11,12); and first and second support portions (M1,M2) formed of a conductive adhesive material to electrically adhere the pair of electrodes (11,12) respectively to the two electrode pads (7,8), the first and second support portions (M1,M2) being provided to support one of the two sides of the first pair of opposing sides on the back surface of the piezoelectric vibration piece, wherein an auxiliary support portion (s) is further provided, the auxiliary support portion (s) being formed of an adhesive material for adhering, in a predetermined adhesive region, at least a point of the piezoelectric vibrating piece near the other of the two sides of the first pair of opposing sides of the back surface thereof to the upper surface of the base member, the auxiliary support portion (s) supporting the piezoelectric vibration piece at the position near the other one of the two sides of the first pair of opposing sides on the back surface thereof, and a position of the auxiliary support portion (s) relative to the other of the two sides of the first pair of opposing sides is set to a position at which a value of (H+D)/L expressed in percentage is equal to or smaller than 20% and H/L expressed in percentage is at least 2%, where L is a distance between the first pair of opposing sides, H is a distance from the other of the two sides of the first pair of opposing sides to a peripheral edge of the auxiliary support portion nearest to the other of the two sides of the first pair of opposing sides, and D is a distance between the peripheral edge of the auxiliary support portion nearest to and a peripheral edge of the auxiliary support portion farthest from the other of the two sides of the first pair of opposing sides in a direction along a virtual centerline connecting center points of the opposing sides of the first pair of opposing sides. a piezoelectric vibration piece having an outer shape rectangular in plan view and provided with driving electrodes (9,10) on front and back main surfaces thereof, the piezoelectric vibration piece further including a pair of electrodes (11,12) for respectively extracting the driving electrodes (9,10) toward one of a first pair of opposing sides of two pairs of opposing sides forming the rectangular shape; a base member having two electrode pads (7,8) on an upper surface thereof, the electrode pads (7,8) being respectively connected to the pair of electrodes (11,12); and first and second support portions (M1,M2) formed of a conductive adhesive material to electrically adhere the pair of electrodes (11,12) respectively to the two electrode pads (7,8), the first and second support portions (M1,M2) being provided to support one of the two sides of the first pair of opposing sides on the back surface of the piezoelectric vibration piece, wherein an auxiliary support portion (s) is further provided, the auxiliary support portion (s) being formed of an adhesive material for adhering, in a predetermined adhesive region, at least a point of the piezoelectric vibrating piece near the other of the two sides of the first pair of opposing sides of the back surface thereof to the upper surface of the base member, the auxiliary support portion (s) supporting the piezoelectric vibration piece at the position near the other one of the two sides of the first pair of opposing sides on the back surface thereof, and a position of the auxiliary support portion (s) relative to the other of the two sides of the first pair of opposing sides is set to a position at which a value of (H+D)/L expressed in percentage is equal to or smaller than 20% and H/L expressed in percentage is at least 2%, where L is a distance between the first pair of opposing sides, H is a distance from the other of the two sides of the first pair of opposing sides to a peripheral edge of the auxiliary support portion nearest to the other of the two sides of the first pair of opposing sides, and D is a distance between the peripheral edge of the auxiliary support portion nearest to and a peripheral edge of the auxiliary support portion farthest from the other of the two sides of the first pair of opposing sides in a direction along a virtual centerline connecting center points of the opposing sides of the first pair of opposing sides.