To detect the press failure of a molded product on the basis of AE produced from the material to be processed during processing without being affected by the disturbance such as a mechanical sound or the like of a press processing apparatus.

The elastic wave produced during molding processing of a material 9 to be processed is detected at the position approaching the material 9 to be processed by a first AE sensor 31 and also detected at the position separated from the material 9 to be processed from a first AE sensor 31 by a second AE sensor 32; these elastic waves are converted to electrical signals to acquire first and second AE waveforms expressing the magnitude of the elastic waves as the change of the voltage value with the elapse of time and the first and second AE energy values being the integrated values of those elastic waves are calculated with respect to a single or a plurality of preset time regions. Then, the ratio of the first and second AE energy values and the ratio of the first and second AE energy values preliminarily calculated with respect to a good product are compared to determine the presence of press failure.

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