A terminal for generating an electromagnetic field adapted to cooperating with at least one transponder when the latter enters its field and including an oscillating circuit adapted to receiving a high-frequency A.C. excitation voltage, circuitry for regulating the signal phase in the oscillating circuit with respect to a reference value, circuitry for determining an instantaneous information relative to the magnetic coupling between the transponder and the terminal, and circuitry for adapting the electromagnetic field power according to at least said present information.