Radio communication system searching method

The invention provides a radio communication system searching method for a portable telephone terminal for selecting, when a plurality of radio communication systems having different carrier frequencies are present in a same area, a suitable one of the radio communication systems. The searching method is improved in that radio communication systems can be searched in order beginning with a radio communication system which is the most advantageous to the user to eliminate the problems of a disorder of company types of radio communication systems and system selection involved in adjacent systems of a same company type. After preferential order numbers of a plurality of radio communication systems are registered into the portable telephone terminal, a home radio communication system of a predetermined frequency with which the portable telephone terminal is under contract is first searched, and then, when the home radio communication system has not been searched out successfully, the remaining radio communication systems are successively searched in accordance with the preferential order numbers registered in advance in the portable telephone terminal.