Objects of the present invention is to provide a piezoelectric resonator having high frequency stability and a sensing sensor using the piezoelectric resonator.In the present invention, a piezoelectric resonator 1 has: a first oscillation area 105 which is provided in a piezoelectric piece 100 and from which a first oscillation frequency is taken out; a second oscillation area which is provided in an area 105 different from the first oscillation area 106 via an elastic boundary area 107 and from which a second oscillation frequency is taken out; and excitation electrodes 101 to 103 provided on one surface side and another surface side of the oscillation areas 105, 106 across the piezoelectric piece 100, and a frequency difference between the first oscillation frequency and the second oscillation frequency is not less than 0.2% nor greater than 2.2% of these oscillation frequencies.