PURPOSE: To provide an S/N ratio optimizing tuning system which can be used in any system comprising a resonance antenna, an amplifier and a single adjustable tuning element, by which the need of separating the amplifier at the time of normally using a receiving antenna can be eliminated.

CONSTITUTION: A S/N ratio optimizing tuning system comprises a switch control noise source 20 weakly connected to a receiving antenna 30, and the switch control noise source 20 is switched from/to the high power state to/from the low power state by means of a designated frequency. A noise power meter 40 is synchronized with the switch control noise source 20, and the output of the receiving antenna 30 is measured. When the noise source 20 is switched to the high power state to the low power state, the noise power meter 40 measures the output of the receiving antenna 30, and the ratio of the output of the receiving antenna 30 when the noise source is in the high power state to the output of the receiving antenna 30 when it is in the low power state is calculated to obtain the noise power ratio. A tuning circuit 70 is adjusted to maximize the noise power ratio.