In order to construct an anechoic chamber satisfying international standards for EMI testing, it has been recognized that the absorption characteristics of the EM wave absorber must be higher than 20dB over the frequency band from 30MHz to 18GHz. In this paper, an EM wave absorber with super wide-band frequency characteristics is proposed and designed in order to satisfy the above requirements by using the EMCM and FDTD. As a result, the proposed absorber has absorption characteristics higher than 20dB over the frequency band from 30MHz to more than 20GHz.