A steam generation boiler having a reaction chamber formed by a bottom portion in a lower portion, a roof portion at an upper portion, and walls extending vertically between the bottom portion and the roof portion. The walls include vertical end walls having a tapering wall section that tapers symmetrically with respect to its middle axis towards the bottom portion, in which (i) a first group of steam pipes in the tapering wall section including steam pipes on both sides of the middle axis, pass at an angle with respect to the middle axis in a wall plane of the tapering wall section, and from the wall plane into the reaction chamber, and (ii) a second group of steam pipes arranged to pass to the bottom portion along the wall plane.