The apparatus of the present invention for determining existential conditions of objects on a certain detecting region, includes: a temperature distribution detecting section for obtaining a thermal image including a plurality of elements each having temperature data by detecting the temperature distribution on the detecting region; an element classifying section for classifying the plurality of elements in the thermal image into at least two groups, all elements belonging to one of the groups being in a certain temperature range, the temperature range of the one group being distinct from a temperature range of another one of the groups; a group selecting section for selecting at least one group of a relatively higher temperature range in the thermal image from the at least two groups; an element selecting section for selecting, among elements included in the selected group, elements having temperature data indicative of local temperature peaks in the thermal image; and an output section for outputting the number of the selected elements by the element selecting means as the number of objects on the detecting region.