A flow-rate sensor is provided with a lead frame, a semiconductor chip that is disposed on one surface of the lead frame, and in which a diaphragm including a void portion on the lead frame side is formed, a flow rate detecting unit that is formed on the one surface including the diaphragm of the semiconductor chip, and resin that includes a flow passage opening portion exposing at least a portion of the flow rate detecting unit formed on the diaphragm, and covers the lead frame and the semiconductor chip. A lower side resin portion of the resin covering another surface side of the lead frame, on an opposite side to the one surface side thereof, has a thinned portion that is thinner than a periphery thereof in a region facing a peripheral edge portion of the diaphragm.