A flow-path forming gasket is interposed between peripheries of each adjacent ones of stacked heat transfer plates; communicating-path forming gaskets are each installed, surrounding the passage holes in each adjacent ones of the heat transfer plates alternately; and thereby a first flow path adapted to pass a high-temperature fluid, a second flow path adapted to pass a low-temperature fluid, and communicating paths adapted to cause the fluids, respectively, to flow in and out of the first and second flow paths are formed alternately on opposite sides of each heat transfer plate. A drain hole is formed in each of the heat transfer plates to discharge fluid leaking from the first flow path, the second flow path, or the communicating path. The drain hole is surrounded by gaskets isolated from the first flow path, the second flow path, or the communicating path. A leakage flow path or a leakage collector is formed by the gaskets.