PURPOSE: To obtain a wide space in a boat shaped in one body by FRP by bending a deck member concavely fitted into the boat toward outside horizontally for shaping staged parts after the member is perpendicularly risen from a floor and providing rising walls to be connected to the upper edge of a gunnel.

CONSTITUTION: For fixing a deck member shaped by FRP in the center of a hull of a fishing boat or the like shaped in one body by FRP, the deck member is bent toward outside horizontally to shape staged parts 5 after it is risen from a floor 2 in sides of the bows, stern, and both sides respectively and perpendicularly, and rising walls 6 are provided to be connected with the upper edge of a gunnel 7. Staged parts 5 are shaped in the height to be in one plane with the upper face of a bow thwart on the bow side and the upper face of a stern thwart on the stern side. This construction permits to use the space in the boat effectively and simplify the manufacturing of the hull.