A plate heat exchanger includes heat transfer plates each of which has openings at four corners thereof, and which are stacked together. The heat transfer plates are partially brazed together such that a first flow passage through which first fluid flows and a second flow passage through which second fluid flows are alternately arranged, with an associated heat transfer plate interposed between the first and second flow passages. The openings at each of the four corners communicate with each other, thereby forming a first header and a second header, the first header allowing the first fluid to flow into and flow out of the first flow passage, the second header allowing the second fluid to flow into and flow out of the second flow passage.