The invention provides a steam boiler which comprises an upper boiler barrel, a lower boiler barrel, ascending pipes and descending pipes. The ascending pipes and the descending pipes are connected between the upper boiler barrel and the lower boiler barrel. Flow stabilizing devices are arranged in the ascending pipes. Each flow stabilizing device comprises a core body and a shell, wherein the core body is arranged in the shell, the shell is connected and fixed to the inner wall of the corresponding ascending pipe, and the core body is formed by adjacently connecting a plurality of pipes in a combined mode. According to the steam boiler, the flow stabilizing devices are of novel structures; and when vapor-water two-phase flow exists in the ascending pipes, heat transfer is enhanced, meanwhile, the vibration of the ascending pipes is weakened, and the noise level is reduced.