to the paging signal step c more specifically the signal coding section 71 encodes the radio condition report signal to output it to the modulation circuit 4 the modulation circuit 4 converts the coded radio condition report signal to a radio transmission signal which is transmitted to the base station through the transmission section 2 and the antenna 1 upon receipt of the radio condition report signal from the portable telephone the base station selects a communication radio channel suitable for the portable telephone and sends a radio channel designation signal to the portable telephone step d when the portable telephone receives the radio channel designation signal from the base station the control section 7 controls the reception circuit 3 so that the reception circuit 3 can receive a radio signal having a frequency of the designated radio channel after the channel is switched to the radio channel designated by the base station the reception circuit 3 receives a call setup signal from the base station step e the call setup signal includes in most cases the telephone number of the caller though this depends on the telephone type on the caller side after receiving the call setup signal the portable telephone sends a call signal as a response signal to the call setup signal to the base station step f upon receipt of the call signal from the portable telephone the base station sends a ringing tone to the caller to inform the caller that the portable telephone takes the call step g after sending the call signal to the base station the reception level measuring circuit 5 of the portable telephone measures a reception electric field intensity of each of the neighboring radio channels previously specified.