To predict disqualification of quality of a product from a change in time series data of an operation factor in a manufacturing process such as an iron and steel process.

This quality disqualification prediction device in the manufacturing process of changing the operation factor is composed of a fractal dimension calculating device for calculating a fractal dimension with process time series data as input, a characteristic quantity calculating device for calculating a characteristic quantity for expressing a change in data with time series out put data of the fractal dimension calculating device as input, and a predicting device for predicting qualification and disqualification of quality with output data of the characteristic quantity calculating device as input. Thus, the fractal dimension is calculated from the process time series data on the inputted operation factor, and its change quantity is converted into a characteristic quantity as a variation per the data score number, and the disqualification of quality of the product is predicted.