Plate heat exchanger and heat pump apparatus including the same

When, out of adjacent two in a stacking direction of heat transfer plates, one heat transfer plate provided in front of the other heat transfer plate is referred to as a first heat transfer plate and the other heat transfer plate provided in rear of the one heat transfer plate is referred to as a second heat transfer plate, a header portion of each of the first heat transfer plates and a corresponding header portion of each of the second heat transfer plates partly form a non-flow path region where the header portions are in contact with each other not to allow fluid to pass through the non-flow path region. A peripheral edge part in the non-flow path region of each of the first heat transfer plates includes a convex portion projecting upward, and a peripheral edge part in the non-flow path region of each of the second heat transfer plates includes a concave portion recessed downward. A space of the convex portion and a space of the concave portion are stacked on each other in the stacking direction to define a cavity, and a communication port through which the cavity communicates with outside is provided at plate portions defining the cavity.