In the present invention, a heating plate is divided into a plurality of regions. Integrated values of temperature fluctuations in each of the regions when a substrate is mounted on the heating plate in a normal state without extraneous matter are collected. A Mahalanobis reference space in the discriminant analysis method is formed based on the integrated values at normal time. During actual heat processing, an integrated value of temperature fluctuation of each of the regions when the substrate is mounted on the heating plate is then detected, so that a Mahalanobis distance about the integrated value during the processing is calculated based on the integrated value during the processing and the Mahalanobis reference space obtained in advance. Whether or not there is extraneous matter on the heating plate is determined by comparing the calculated Mahalanobis distance to a predetermined threshold value.