The circular polarized antenna composed of an unbalanced fed ultra low profile inverted L antenna and L shaped slot is proposed for the reader antenna of the portable terminal of RFID. At UHF band from 915 MHz to 930 MHz, the condition make the circular polarization is the S_<11> less than -10dB and axial ratio less than -3dB. The analysis model met this condition. In the numerical analysis, the electromagnetic simulator "WIPL-D" based on method of moment is used.