To provide a water tube boiler which can achieve reduction of size and reduction in the generation of NOx by a can body.

A water tube 15 for heat recovery is situated in the vicinity of a water tube train 9 to partition a combustion chamber 10. Furthermore, gas flow gaps 12 are situated between water tubes 8 in a given spot of the water tube train 9, and the water tube 15 for heat recovery is situated, facing the given gas flow gap 12 of the gas flow gaps 12.