A plate heat exchanger comprising a body portion that includes a plurality of heat transfer plates stacked on each other, the body portion further including a plurality of first flow channels that circulate a first fluid medium, a plurality of second flow channels that circulate a second fluid medium, a pair of first communication flow channels (32, 33) that communicate with the plurality of the first flow channels and allow the first fluid medium to flow into and out of the plurality of the first flow channels, a pair of second communication flow channels (34, 35) that communicate with the plurality of the second flow channels and allow the second fluid medium to flow into and out of the plurality of the second flow channels, the plurality of the first flow channels and the plurality of the second flow channels being alternately formed with the plurality of the heat transfer plates being respectively interposed therebetween, and the pair of first communication flow channels (32, 33) and the pair of second communication flow channels (34, 35) extending in the stacked direction of the plurality of the heat transfer plates through the plurality of the heat transfer plates, wherein the plurality of the first flow channels communicate with each other to form a flow channel of the first fluid medium from one of the pair of first communication flow channels (32, 33) to the other of the pair of first communication flow channels (32, 33), wherein at least one of the plurality of the first flow channels is a reference flow channel (Ra) that serves as a starting point of the flow channel of the first fluid medium, wherein the one of the pair of first communication flow channels (32, 33) communicates only with the reference flow channel, and wherein the other of the pair of first flow channels (32, 33) communicates only with a plurality of the first flow channels, the number of the plurality of the first flow channels being greater than the number of the reference flow channel (Ra), and the plurality of the first flow channels serving as a terminal end of the flow channel of the first fluid medium, characterized in that at least one the plurality of the first flow channels located at an intermediate position in the stacked direction of the plurality of the heat transfer plates is a reference flow channel (Ra) which serves as a starting point of the flow channel of the first fluid medium, wherein the body portion includes at least one pair of primary branch flow channels that provide communication between the reference flow channel (Ra) and at least one first flow channel located on each of the one side and the other side of the reference flow channel (Ra) in the stacked direction of the plurality of the heat transfer plates, and wherein the other of the pair of first communication flow channels (32, 33) communicates only with a plurality of first flow channels which serve as a terminal end of the flow channel of the first fluid medium on each of the one end and the other end of the reference flow channel (Ra) in the stacked direction of the plurality of the heat transfer plates, the number of the plurality of first flow channels being greater than the number of the reference flow channel (Ra).