A boiler structure, wherein pressure losses (friction losses) occurring between furnace inlet headers and outlet headers are reduced by appropriately distributing, without an excessive increase in pressure losses, the flow rates of internal fluid flowing on a furnace wall surface (water-cooled wall) divided into furnace wall sections. In the boiler structure, the water-cooled furnace wall (4) comprises a large number of boiler evaporating tubes (3) disposed on the wall surface of a furnace, and vapor is generated by heating water sent under pressure to the boiler evaporating tubes (3) in the furnace when the water flows in the tubes. The boiler structure comprises orifices (22) adapted for the internal fluid and formed in inlet connection tubes (20) for leading the water to the inlet headers (21) of the furnace wall sections formed by dividing the water-cooled furnace wall (4), and orifices (23) provided at tube base sections for leading the water from the inlet headers (21) to the boiler evaporating tubes (3).