A piezoelectric sensor for measuring an external force is disclosed which is accommodated in a cassette through a sealing member and provided with a pair of electrodes which are respectively bonded to opposite sides of a piezoelectric element. A masking strip made of a highly insulative material covers the whole area of and end face of the piezoelectric element, which is exposed to the outside of the sensor, and a desired width of an end face of each of the electrodes adjacent to the end face of the piezoelectric element. This maintains a high resistance between the electrodes having the piezoelectric element therebetween and thereby promotes accurate measurement without being effected by changes in the resistance of the sealing member due to temperature variation. The sensor is effectively applicable to a vortex flow meter.
