To provide a noncontact IC card device for electronic settlement system that realizes the reduction of interferen with other system and the deduction of the power consumption.

The noncontact IC card device for electronic settlement system includes a radio transmitting and receiving circuit 101 which transmits and receives digital information about electronic transactions to and from a noncontact reader/writer by use of weak radio waves of specific lower power radio waves; a storage circuit 104 for storing information including the digital information which the noncontact reader/writer receives from the radio transmitting and receiving circuit 101; a display part 102 for displaying choices about the electronic transactions according to the digital information; a cursor key 105 for moving a cursor displayed in the display part 102; a selecting key 106 for selecting either of the choices of the digital information displayed in the display part 102, by determining the choice designated by the cursor; a control circuit 103; and a transmit power control circuit for optimally controlling the transmit power of the radio transmitting and receiving circuit 101 according to the distance and positional relationship between the radio transmitting and receiving circuit 101 and the noncontact reader/writer and the condition of ambient radio waves.