This invention relates to an automatic detection apparatus for UL/DL configuration in LTE-TDD signal and the method thereby for automatically detecting the UL/DL configuration number of an LTE-TDD signal without a decoder by using a simple structure. An automatic detection apparatus for UL/DL configuration in LTE-TDD signal comprises: a signal receiving unit for receiving an LTE-TDD RF signal and converting the LTE-TDD RF signal into a LTE-TDD baseband signal; a signal extracting unit for extracting a cell-specific reference signal for each subframe length in one frame length of the LTE-TDD baseband signal received from the signal receiving unit; a signal power measurement unit for measuring the power of the corresponding subframe reference signal according to the cell-specific reference signal received from the signal extracting unit; and an UL/DL configuration determination unit for determining whether the corresponding subframe is a DL subframe or an UL subframe according to the comparison result of the power of the corresponding subframe reference signal measured in the signal power measurement unit with a predetermined reference value, and determining the UL/DL configuration number for the corresponding frame based on the subframe number determined as described above. In the above configuration, it is characterized in that the predetermined reference value is the noise power without any LTE-TDD signal.