PURPOSE: To heighten measurement precision and position resolution by continuously laying down a transmission route of an optical fiber at each measurement point of an area to be measured, applying a signal for reference and continuously and exactly measuring temperature, humidity and temperature distribution of a lot of measurement points.

CONSTITUTION: A conduit 15 is hung from a ceiling 21 as a thermal partition wall in a room which is an area to be measured, arranged in the room, optical fibers 13 are passed therein, the optical fibers are loosely drawn from branch pipes 161-16n of the conduit 15 respectively provided at a plurality of temperature measurement points and temperature measurement parts 171-17n which indicate the same wound method as a non-inductive resistance are pulled from the branch pipes 161-16n to the outside. An operation instruction is received from CPU of a signal processor 14 of a thermometer body 20, and a light pulse emitted from a light source 11 is made incident on the optical fibers 13 through a beam splitter 12. Back scattered light is returned from each temperature measurement part 171-17n, introduced to the signal processor 14 through the beam splitter 12 and temperature is measured from the intensity of the back scattered light at the positions of the temperature measurement parts and therefrom.