To provide a gas short circuit pass preventive baffle for effectively preventing a gas short circuit pass between tube blocks and easily mounted in a heat exchanger having a plurality of the tube blocks for heat exchanging aligned at a gas channel for heat exchanging.

The gas short circuit pass preventive baffle 20 comprises a C-shape steel 26, and L-shape steels 28 aligned and disposed along a length direction of the steel 26 in the same bending direction on both surfaces of the steel 26. The steels 28 are disposed at an interval between the adjacent steels 28 and connected to the steel 26 by welding 30 at one side of edges along the length direction. The baffle 20 is supported at its upper part by a hanging bar 32, and vertically slidably supported at its lower part to a lower stopper 34.