The present invention relates to a boiler furnace for a power station, in which the combustion space formed by an outer water tube unit and an inner water tube unit has a shape conforming to the natural shape of a flame to increase the contact area with the flame, and water and steam heated by the outer water tube unit are supplied to the inner water tube unit to raise the temperature of water being heated in the water tube unit of the furnace, and thus improve heat efficiency. The boiler furnace of the present invention comprises an outer water tube unit which receives water from an external source and heats the received water to high-temperature water (including steam) while enabling the water to flow in an upward direction, and an inner water tube unit disposed in the outer water tube unit to receive water from an external source and to heat the received water to high-temperature water (including steam) while enabling the water to flow in an upward direction. The outer water tube unit has a diameter which is gradually widened from or almost identical to the bottom thereof to the center (M) thereof. Then, the diameter of the outer water tube unit becomes narrow, then becomes wide, and becomes narrow again from the center thereof to the top thereof. The inner water tube unit has a diameter which gradually becomes narrow and then becomes widened from the bottom thereof to the center (M) thereof. Then, the diameter of the inner water tube unit becomes narrow, then becomes wide, and becomes narrow again from the center thereof to the top thereof. The combustion chamber formed between the outer water tube unit and the inner water tube unit is gradually widened and then becomes narrow from the bottom thereof to the center (M) thereof, and is curved from the center thereof to the top thereof.