To provide a noncontact type IC tag capable of surely checking information about occurrence of a prescribed change in a temperature environment and being made difficult to falsify the information, without having any power source nor using any special measuring instrument, like a conventional sensor tag having a function of detecting temperature without any power source.

A temperature change detecting section is composed of a temperature change memory type switching element; a nonvolatile memory section which is disposed inside an IC chip of an noncontact data carrier and used for storing temperature information; and a memory control circuit section which controls writing and reading operations for the nonvolatile memory. The temperature change detecting section uses voltage as its power source which is generated by energy supply from an external circuit, senses an ON-OFF state of the above switching element as its voltage level, accepts the voltage level in its ON state as a write-in command signal for the memory control circuit section, and writes temperature information representing a temperature change into the nonvolatile memory section under the control of the memory control circuit section, in the case the above write-in command signal exists.