To provide a heat recovery boiler for exhaust gas to which fly ash contained in exhaust gas hardly adhere and which is hardly corroded by carbon monoxide.

This heat recovery boiler for exhaust gas is provided with side walls constituting an n-polygon (wherein, n is an integer of ≥8) or a circule in a cross section perpendicular to the flowing direction of the exhaust gas and the internal surface of which is coated with SiC-based castable refractory having a thickness of 40-80 mm.