A piezoelectric sensor is fixed to a detection object and detects distortion of the detection object includes first and second principal surfaces, and extends in the lengthwise direction. The piezoelectric sensor includes a piezoelectric body whose polarization axis extends in a direction parallel or substantially parallel to the lengthwise direction, and first and second detecting electrodes that are provided on a surface of the piezoelectric body and that extend in a direction parallel or substantially parallel to the lengthwise direction. Distortion of the detection object is detected based on electric output corresponding to shear stress of the piezoelectric body.