The application of ultrasound, which has been shown to be useful for the supercooling relaxation and solidification enhancement of erythritol as an organic phase change material in our previous study, was further investigated. Experiments on the solidification of erythritol were conducted using a visualization setup with a cooling vertical double-pipe. Functions of ultrasonic irradiation parameters, in particular, amplitude and irradiation mode in relation to its physical effects were investigated. It was shown that melt with a higher degree of supercooling facilitates the crystal formation in the presence of ultrasound. Together with the rapid propagation of crystals by secondary nucleation and effective bulk mixing, restoration of supercooled melt to its melting temperature was promptly attained at higher acoustic amplitudes. Pulsed and continuous irradiation modes were compared. The results demonstrated that continuous irradiation led to sustained secondary nucleation. In other words, ultrasonic irradiation enabled constant fragmentation and effective dispersion of crystals by the mixing of erythritol melt.