Frequency response calculation was carried out for a continuous cooling crystallizer where cooling temperature and crystal production rate are regarded as input and output, respectively. It was found that appropriate selection of amplitude and augular frequency almost stabilized sustained oscillation of the crystal production rate. To explain this phenomenon, the theory of signal stabilization was introduced. Based on this theory, it was interpeted that sustained oscillation was due to a strong nonlinearity of nucleation rate and that these nonlinear characterestics enabled us to reduce sustained oscillation by cooling temperature input with suitable amplitude and angular frequency. From this fact, it was recognized that the theory of signal stabilization was useful to the control system design of continuous crystallizer which showed sustained oscillation.