In a primary heat exchanger, a heat conduction pipe is arranged as one connected pipe in a lower stage and an upper stage in a manner extending back and forth through a plurality of fins. The heat conduction pipe is arranged such that a pitch between the heat conduction pipes in the upper stage is shorter than a pitch between the heat conduction pipes in the lower stage. In addition, the heat conduction pipe is arranged such that a position in a center of each heat conduction pipe in the upper stage in a second direction orthogonal to a first direction in which the heat conduction pipe extends and a position in a center of each heat conduction pipe in the lower stage in the second direction are displaced from each other.