In the hydrocarbon-producing apparatus, a vapor-liquid separation tank of a second vapor-liquid separation unit is provided with a filling material layer. A vapor-liquid separation tank of the first vapor-liquid separation unit has a first return line. The vapor-liquid separation tank of the second vapor-liquid separation unit has a second return line. A light component of light oil discharged from a bottom of the vapor-liquid separation tank is returned to a portion between a top side above a return-location from the second return line within the vapor-liquid separation tank of the second vapor-liquid separation unit, and a line directly connected with a cooler installed on the first vapor-liquid separation unit through the first return line. A heavy component of light oil discharged from a bottom of the vapor-liquid separation tank of the second vapor-liquid separation unit is returned to the filling material layer through the second return line.