Disclosed herein are an apparatus and method for collecting vehicle diagnostic information. The apparatus for collecting vehicle diagnostic information includes a conversion unit and an optical multiplexing unit. The conversion unit receives a plurality of frames complying with respective different protocols from a plurality of networks for vehicles, which collects vehicle diagnostic information, in electric signal form, and converts the plurality of frames into a plurality of optical signals having respective different wavelengths based on the wavelengths previously assigned to the respective protocols. The optical multiplexing unit generates a wavelength division multiplexed signal by performing wavelength division multiplexing (WDM) on the plurality of optical signals, and transmits the wavelength division multiplexed signal via an optical cable.