A mobile radio terminal 10 is adaptable to two kinds of mobile telephone systems A and B given priorities as A>B. When the mobile radio terminal (10) is located at a position M1, location registration is carried out between the mobile radio terminal (10) and the system B and the mobile radio terminal (10) is in a standby state in the system B. When the mobile radio terminal (10) moves to another position M2 and detects a cell of the system A by cell search (periodic) for the system A, location registration is carried out between the mobile radio terminal (10) and the system A and the mobile radio terminal (10) is turned into a standby state in the system A. If a user executes a "transmission-related operation", cell search is immediately carried out to put the mobile radio terminal (10) into the standby state in the system A.