A plate heat exchanger includes a stack of a plurality of plates each having an inlet and an outlet for a fluid. Each adjacent two of the plates are bonded to each other at regions thereof where top parts of the wavy portion provided in a lower one of the plates and bottom parts of the wavy portion provided in an upper one of the plates overlap each other when seen in the stacking direction. Particularly, a top part included in the top parts of the wavy portion of the lower plate and being adjacent to each of the inlet and the outlet has a planar shape.