A casing structure for chromatograph having a plurality of casings respectively installing at least a separating column, a sample inducing portion and/or a detector portion of the chromatograph and the casings are vertically stacked one on another or horizontally juxtaposed one to another. The casing structure further comprises a passage for installing reagent feed pipes therein, and the passage is respectively provided in respective side portions of the casing for communicating with that of another casing when in the stacked state or in the juxtaposed state, and has an inner hole at an inner side thereof for connecting the reagent feed pipes to a pipe connecting portion arranged in the casings, and the passage has a cover at an outer side thereof for being opened outside of the casing.