A latent heat exchanger comprising: a casing having a flow path of combustion gas therein; a heat absorbing pipe accommodated in the casing; an inlet header for introducing fluid to be heated into the heat absorbing pipe; and an outlet header for discharging the fluid to be heated from the heat absorbing pipe, wherein the casing has a box-shaped casing body having an upper opening and a top board closing the upper opening of the casing body, the casing body has a back wall, a front wall, a bottom wall having a drain discharging opening, one side wall having an upstream end-inserting hole through which an upstream end of the heat absorbing pipe is inserted and a downstream end-inserting hole through which a downstream end of the heat absorbing pipe is inserted, and another side wall, the back wall, the front wall, the bottom wall, the one side wall, and the other side wall are integrally formed by drawing one single metal plate, the heat absorbing pipe in the casing has a piping structure in which a straight portion extending between the one side wall and the other side wall and circularly arcuate turn-around portions located at both ends on one side wall side and the other side wall side are repeated consecutively, and the inlet header and the outlet header are respectively disposed outside the one side wall and connected to the upstream and downstream ends of the heat absorbing pipe led outside the one side wall through the upstream end-inserting hole and the downstream end-inserting hole; and a side baffle plate in a plate shape provided between the circularly arcuate turn-around portions located on the other side wall side and an inner surface of the other side wall, wherein an upper end of the side baffle plate is connected to a lower surface of the top board, and a lower end of the side baffle plate is disposed such that the lower end does not abut an inner surface of the bottom wall. a casing having a flow path of combustion gas therein; a heat absorbing pipe accommodated in the casing; an inlet header for introducing fluid to be heated into the heat absorbing pipe; and an outlet header for discharging the fluid to be heated from the heat absorbing pipe, wherein the casing has a box-shaped casing body having an upper opening and a top board closing the upper opening of the casing body, the casing body has a back wall, a front wall, a bottom wall having a drain discharging opening, one side wall having an upstream end-inserting hole through which an upstream end of the heat absorbing pipe is inserted and a downstream end-inserting hole through which a downstream end of the heat absorbing pipe is inserted, and another side wall, the back wall, the front wall, the bottom wall, the one side wall, and the other side wall are integrally formed by drawing one single metal plate, the heat absorbing pipe in the casing has a piping structure in which a straight portion extending between the one side wall and the other side wall and circularly arcuate turn-around portions located at both ends on one side wall side and the other side wall side are repeated consecutively, and the inlet header and the outlet header are respectively disposed outside the one side wall and connected to the upstream and downstream ends of the heat absorbing pipe led outside the one side wall through the upstream end-inserting hole and the downstream end-inserting hole; and a side baffle plate in a plate shape provided between the circularly arcuate turn-around portions located on the other side wall side and an inner surface of the other side wall, wherein an upper end of the side baffle plate is connected to a lower surface of the top board, and a lower end of the side baffle plate is disposed such that the lower end does not abut an inner surface of the bottom wall.