The pressure wave supercharger includes a housing having an accommodating room to accommodate a rotor rotatably about an axis, and an exhaust side wall face which is arranged at the accommodating room as being opposed to one end face of the rotor and to which an exhaust gas introduction port and an exhaust gas discharge port are opened, and the rotor includes a shaft portion supported by the housing rotatably about the axis, plural partition walls arranged as being extended in the radial direction from the shaft portion and in the axial direction from the one end face to other end face of the rotor, and a partition member which is arranged at a space between adjacent partition walls and which partitions the space into an inner cell and an outer cell as extending from the one end face to the other end face of the rotor, and an exhaust side groove portion concaved in a direction being apart from the rotor is formed at the exhaust side wall face as being overlapped with a trajectory of the partition member lined during rotation of the rotor as viewed from the axial direction.