PURPOSE: To measure weight or the like of a passing material body accurately by providing plural piezoelectric sensors with the necessary length in a line in the direction of the passing of the material body on a passing way of the material body and obtaining a signal in proportion to the pressure from between electrodes of a piezoelectric body.

CONSTITUTION: The piezoelectric sensors 5a and 5b are constituted of the piezoelectric body 6 provided on a base 7, the electrode 8 and a shared electrode 9 having the protrusion 9a provided between the piezoelectric body 6 and the base 7, and the signal in proportion to the pressure is obtained. Then, the piezoelectric sensors 5a and 5b are provided in a line in the direction of the passing of the material body G on the passing way W of the body and connected with a signal processor 11 via amplifiers 10a and 10b. Then, when the material body G moves on the passing way W and presses the protrusion 9a of the piezoelectric sensors 5a and 5b, the signal in proportion to the pressure is obtained from between the electrodes 8 and 9 and processed with the signal processor 11, and the weight, passing direction and velocity of the body G are measured accurately.