A plate-shaped board is arranged so that fluid passages are respectively formed at a sensor-element mounting surface side of the plate-shaped board and at a backside surface side thereof being opposed to the sensor-element mounting surface side, a curved passage portion is provided which is located upstream of the plate-shaped board and changes its direction so as to form a curved line, and the curved passage portion has an outer-side wall surface including a sloping portion that slopes so that, of two edge portions of the outer-side wall surface in a direction perpendicular to board surfaces of the plate-shaped board, the edge portion located on a sidewall surface, facing the sensor-element mounting surface, of the curved passage portion is positioned closer to an inner wall surface of the curved passage portion than the edge portion located on a sidewall surface opposed to the first sidewall surface, along the sidewall surfaces.