A plant monitoring apparatus includes: a process measuring unit; a warning determining unit; a warning selecting unit; a display processing unit; a display/setting unit; a warning criteria setting unit; a warning criteria database; and a warning criteria supplying unit. The warning determining unit determines a plurality of warning data to be issued as warnings from a large amount of process data collected by the process measuring unit on the basis of a predetermined determination criterion. The warning selecting unit compares the plurality of warning data with one or more classification criteria supplied by the warning criteria supplying unit so as to classify the plurality of warning data. Warnings are classified into categories according to the classification and the classified warnings are displayed on the display/setting unit.