To efficiently mold a thermoplastic resin or a thermosetting resin by ultrasonic waves without using a mold.

A liquid tank 1 is filled with a liquid heated up to the vicinity of the softening transition temperature of a thermoplastic resin and the plate- shaped thermoplastic resin 5 is supported on the surface of the liquid to be heated and softened. Ultrasonic waves are oscillated into the heated liquid 3 by the ultrasonic oscillator 7 comprising an ultrasonic oscillation array or phase control plate arranged on the bottom part of the liquid tank 1 and a hologram image is formed on the surface 6 of the liquid by the mutual interference thereof and the thermoplastic resin 5 is molded into a molded part 8 having a predetermined shape along the hologram image by the pressure thereof.