There is provided a tire state monitoring apparatus including transponders mounted on a plurality of tires possessed by a vehicle, and ECUs provided on a vehicle body repeatedly transmit address electric waves for acquiring data showing tire states to the transponders at fixed intervals. The ECUs transmit estimates of the transmission timing of the address electric waves at the predetermined transmission cycle so that the transponders can transmit the address electric waves within a communicable range, maintain the predetermined transmission cycle if the estimated transmission timing satisfies a predetermined condition, and adjust the predetermined transmission cycle if the transmission timing does not satisfy the predetermined condition.