A driving circuit (106) controls a time for applying a drive signal to a piezoelectric element (101) so as to bring a change in the number of ink droplets squirted from a liquid surface of liquid ink (109) according to a gray scale level of an image to be printed on a printed object. According to application of the drive signal, ultrasonic beams emitted from a piezoelectric element array (101) are converged in an array direction, made incident to an acoustic lens (107) via an acoustic matching layer (105), further converged in a direction orthogonal to the array direction and converged in a vicinity of the liquid surface in a point form. In the vicinity of the liquid surface, an ink meniscus (111) is formed by means of pressure (discharging pressure) generated by the converged ultrasonic beams and then from a tip of the ink meniscus (111) an ink droplet according to the application time is squirted. The squirted ink droplet is flown and stuck to the printed object. By performing main and subscanning to the printed object, a two-dimensional image is printed thereon.