A flow sensor (1) is constituted by a substrate (4) having a front surface (4a) side facing a channel (3) for a measurement target fluid (2), and a channel forming member (5) and a plate (6) disposed oppositely across the substrate (4). The substrate (4) is formed of stainless steel having a thickness of about 50 μm to 150 μm into a plate. An electric insulating film is formed on that surface (4b) of the substrate (4) which is opposite to the channel (3) side, and a temperature detection sensor (7) for measuring the flow velocity (flow rate) of the fluid (2), an ambient temperature sensor (8), an electrode pad (9), and a thin metal film (10) for wiring are formed on it.