There is provided a system for changing programs stored in a terminal device, including (a) a base station, (b) a program-transferring device which transfers a program to the base station, and (c) a terminal device which downloads a program thereinto from the program-transferring device through the base station, the terminal device including (c1) a memory storing therein at least two programs grouped into at least two groups with respect to a function of a program, and (c2) a management table which stores first data about whether the programs are used or not, and removes a non-used program from the memory. In accordance with the present invention, it is no longer necessary to write all programs into a memory of a terminal device when a function of the terminal device is to be changed. Hence, a function of the terminal device can be changed merely by writing a necessary part of a program into the terminal device, ensuring that a working time can be shortened.