A connection method includes softening a resin film of a thermosetting resin by heating an element electrode of a piezoelectric body and a substrate electrode of a flexible cable to be connected to the piezoelectric body with the element electrode and the substrate electrode being pressed into contact with each other via the resin film; partially pushing out the molten resin film from an opposing position of the element electrode and the substrate electrode so as to bring a solder layer provided on the substrate electrode into contact with the element electrode; curing the resin film and melting solder in the solder layer by further raising a heating temperature; discharging excess solder in a direction defined by the cured resin film; and then solidifying the solder in the solder layer so as to solder the element electrode and the substrate electrode together.