PURPOSE: To easily change or add a function of a radio telephone set.

CONSTITUTION: A telephone function card 2 can be mounted to a telephone set main body 1. The telephone set main body 1 is provided with a control part 13 and the control part 13 and a memory 14 are connected while the telephone set function card 2 is mounted to the telephone set main body 1. A program is stored in the memory 14 and the control part 13 is operated corresponding to the program based on the operating state of an operation part 9. Thus, by changing the telephone set function card 2, the function of this radio telephone set is easily added or changed.