Provided are a method and device for separating and converting multiband signals. The device includes a photoelectric converter for converting an externally received optical signal into an electrical signal, a first switch for separating the converted electrical signal into signals according to frequency bands, a first mobile communication band-pass amplifier for amplifying a mobile communication network signal of the signals separated by the first switch, a broadband up-converter for up-converting a baseband signal of the signals separated by the first switch into a broadband signal, a first broadband amplifier for amplifying the broadband signal output from the broadband up-converter, and a transmitter for wirelessly transmitting the signals amplified by the first mobile communication band-pass amplifier and the first broadband amplifier.