PURPOSE: To detect easily the accident or bad condition of a machine in its early stages, carrying out the quality control corresponding to the quality of a product by detecting measured values, while measuring the physical quantity with the influence for quality at each molding cycle, and classifying the deviation rate of the measured value correspondingly to its degree.

CONSTITUTION: A measuring part 3 measures the physical quantity such as an injection pressure with the influence for quality at each molding cycle by the timing command of a controlling section 2, using the sensor, etc. for detecting physical quantity, and then detects the data of the measured value. 13 and 14 are the devices for setting allowable deviation range, and the set value corresponding to the value of the deviation range is provided. The set value and the measured value obtained by a sampling measurement, are arithmetically operated, and the reference value for classification is set. An information outputting section 15 is operated by the signal from the arithmetically operating section 4 indicating the classified domain to which the data of the measured value belongs. The data of the measured value is recorded by the sign indicating each classified domain at a printer 16 by said output signal. Accordingly, the quality of the product and the abnormality of the machine are clealy judged.