A processing device (120) of a tire state detection system (100) is provided with an acceleration data acquisition unit (123) for acquiring the acceleration data detected by an acceleration sensor (111) at every predetermined acquisition interval, an acceleration data extraction unit (125) for extracting the maximum acceleration data indicating at least the maximum acceleration and the intermediate acceleration data indicating the intermediate acceleration excluding the minimum acceleration data indicating the minimum acceleration from 3 or more acceleration data acquired sequentially, and a calculation unit (127) for executing an calculation using the extracted intermediate acceleration data.