PURPOSE: To identify a heat detected position with a simple arrangement by using the local microbending loss of a covered optical fiber caused by the contraction of thermo-contracting material.

CONSTITUTION: A thermo-contracting material 3 is arranged in a thermo- contracting material housing part 11A under a state in which only one edge 13a of the material 13 is fixed, and a covered optical fiber 12 is fixed linearly along the thermo-contracting material 13 onto fixing points A and B at both edges of the material 13 in the thermo-contracting material housing part 11A. Consequently, when the ambient temperature becomes high, and the thermo- contracting material 13 contracts by heat, the covered optical fiber 12 meanders between the points A and B, and optical transmission loss caused by microbending increases. Thus, time of day and the place where the ambient temperature of the title fiber type heat sensor rises can be accurately detected by continuously monitoring the longitudinal directional optical transmission loss distribution of the covered optical fiber 12 by a back scattering light measuring instrument.