A heat exchanger for hot water supply (21) is comprised of: a first heat exchanging unit (21) a that heats the water, which is supplied from a second communication section x1 to the hollow portions of hollow plates P1 to P5 and reaches a first communication section y, by a combustion exhaust gas that circulates through the gaps among the hollow plates P1 to P5; and a second heat exchanging unit (21b) that heats the water, which is supplied from the first communication section y to the hollow portions of the hollow plates P6 to P8 below the hollow plates P1 to P5 and reaches a third communication section x2, by a heat medium that circulates through the gaps among the hollow plates P6 to P8.