PURPOSE: To enable the prediction of particularly restraining breakout with high accuracy by detecting the practicable oscillation condition of the mold of a continuous casting installation and detecting the displacement of the safety spring of an oscillation mechanism in combination with said detection.

CONSTITUTION: The practicable oscillation waveform of a mold 1 which is moved vertically by an osicllation mechanism is read with an oscillation detector 16 provided to a mold head 2. The minute displacement in the acting direction of the safety spring 13 in a safety spring device 14 connected to the output shaft 10 of the oscillation mechanism is detected with a micro displacement meter 17 mounted to the device 14. An amplitude (force) comparator 20 takes therein both signals of the detector 16 and the meter 17 and outputs the operation command signal of a display device 25 for predicting breakout to an alarm setter 24 after considering the correction signal for the waste time from a phase corrector 23. The danger of an error in the judgement owing to the influence of disturbance is thus averted.