To estimate the modulation system of a received signal easily in a simple constitution, in a wireless transmission system with an adaptive modulation system, in which a plurality of modulation systems are selected adequately according to the variations in characteristics of the propagation path.

Priority is applied to each modulation system as a candidate for estimation process of the modulation system, and the estimation process is carried out sequentially from the modulation system with high priority. When prescribed likelihood is obtained, the modulation system of the received signal is determined. Then, in a simple constitution, the modulation system of the received signal can be estimated easily.