tank comprising a thick substrate having a cavity structure and a vibrating plate covering a cavity and a piezoelectric electrostrictive working portion comprising an upper electrode layer a lower electrode layer and a piezoelectric electrostrictive layer between the electrode layers the piezoelectric electrostrictive working portion being disposed on the ink tank so that the lower electrode layer contacts with the vibrating plate the upper electrode is trimmed only in the portion where the piezoelectric electro strictive layer covers the vibrating plate so as to control an effective electrode area and adjust an ink jet volume to be appropriate the upper electrode layer is trimmed with the piezoelectric electrostrictive layer covering the vibrating plate at least near the portion to be trimmed of the upper electrode layer so as to control an effective electrode area and adjust an ink jet volume application_number US 93225997 A description an actuator for an ink jet printer of the present invention is hereinbelow described in detail with reference to drawings fig1 a and 1 b are structural views showing an embodiment of an actuator of the present invention fig1 a is a plan view and fig1 b is a cross sectional view in fig1 a and 1 b a thick substrate 21 has a cavity 20 a vibrating plate 22 is formed unitarily with the thick substrate 21 so that the vibrating plate 22 covers the cavity 20 on the upper surface of the vibrating plate 22 were superposed a lower electrode 23 a piezoelectric electrostrictive layer 24 and an upper electrode layer 25 in this order so as to form a piezoelectric electrostrictive working portion 26 the upper electrode layer 25 is cut by trimming at a line.