Actuator elements are accommodated in openings formed in a conductive plate. These actuator elements are secured to the conductive plate by a resin bonding material. An electrode of each actuator element and the conductive plate are electrically connected to each other by a bridge junction consisting of an conductive paste. A paste application device discharges the conductive paste toward the bridge junction by air. A control unit configured to control the discharge of the conductive paste sets the air pressure according to the elapsed time of use of the conductive paste so that the height of the paste above the resin bonding material is not less than a target height. The target height is maintained by increasing the air pressure with increase of the elapsed time of use of the conductive paste.