In order to detect an abnormality of semiconductor manufacturing apparatus, a biaxial coordinate system having first and second axes respectively assigned two different monitoring parameters selected from plural apparatus status parameters representing statuses of semiconductor manufacturing apparatus is prepared. As monitoring parameters, for example, a cumulative film thickness for deposition processes that have previously been performed in deposition apparatus and an opening of the pressure control valve located in a vacuum exhaust path to control the internal pressure of a reaction vessel are selected. Values of monitoring parameters obtained when the semiconductor manufacturing apparatus was normally operating are plotted on the biaxial coordinate system. A boundary between a normal condition and an abnormality status is set around a plot group. Values of monitoring parameters obtained during present operation of the semiconductor manufacturing apparatus are plotted on the biaxial coordinate system to determine whether or not there exists an abnormality and identify a type of abnormality based on a positional relation between the plots and the boundary.