An inner gear includes an insertion hole, which extends through the inner gear in an axial direction, and a first balance groove, which is axially recessed at an axial end portion of the inner gear and is communicated with the insertion hole. First and second chamfered portions are formed in an inner peripheral edge of the inner gear, which is adjacent to the insertion hole. A joint member has a leg inserted into the insertion hole. An inserting direction of the leg into the insertion hole is defined as a first direction, and a direction, which is opposite from the first direction, is defined as a second direction. In a view taken in a direction perpendicular to the axial direction, at least a part of a first direction side end portion of the leg is axially placed between a first chamfered end plane and a first groove end plane.