A detected temperature acquiring portion acquires detected temperatures from individual thermopile array sensors, a temperature change comparing portion compares changes in detected temperatures over time, for each respective location, between test locations selected from a overlapping region and individual comparing locations for two thermopile array sensors wherein planned detecting ranges partially overlap each other, to identify a best match location, a factor estimating portion, for each test location, generates an equation indicating a relationship between the best match location and positional shift factors, and establishes these equations as a system and solves the system of equations through a least-squares method to estimate the positional shift factors, and a detecting range identifying portion corrects location coordinates of the planned detecting ranges based on these positional shift factors to identify actual detecting ranges.