The resonant inductive coupling wireless power transfer technique (RIC-WPT) is emerging as a promising wireless power transfer method for small mobile devices with comparatively high-power transfer capability and good efficiency. However, the performance of the RIC-WPT system is severely deteriorated by the resonant frequency detuning of the transmitter, repeater, and receiver resonators, which can be naturally caused by the manufacturing tolerance and the aging effect of these resonators. Particularly, the detuning of the repeater resonator tends to severely affect the performance due to its high-quality factor, which should be solved for practical application of RIC-WPT technology. This paper addresses this difficulty by proposing an autonomous resonant frequency tuning controller circuit for the repeater resonator. The controller tunes the resonant frequency of the repeater resonator to the operating frequency of the inverter, driving the transmitter, without an external power supply and wireless communication with the inverter controller, which restricts the freedom of the installation location and therefore preferably be avoided in the wireless power transfer system. The operating principles of the proposed controller were confirmed by the circuit simulator, supporting the feasibility of the proposed controller.