PURPOSE: To achieve sufficient water-tightness of each panel while to perform opening/closing of panel smoothly by inclining the guide rail for a guide travel wheel of a foldable hatch cover downward gradually as departing from the section near to the folding container table.

CONSTITUTION: The guide rail 20 for guide travel wheels 151W154 provided at the side of panel of hatch cover constructed such that the hatch panel is coupled through rotatable ends will be foldable is inclined downward as departing from the section near to the folding container table. Each step (h) of down ward inclination has such height as necessary for the gasket of each panel to release the compression bar upward from compressed state thus to achieve sufficient water- tightness due to each panel while to smooth opening/closing of the panel.