A temperature-sensitive sensor (21) and a heating temperature-sensitive sensor (22) are fixed in position in a liquid-tight fashion by welding, with the metal tubular bodies (36 and 37) being inserted into the tubular body insertion holes (19 and 20) of a vortex detector (4). Sealing performance is secured without using any O-ring. The temperature-sensitive sensor (21) and the heating temperature-sensitive sensor (22) respectively have lead wires (42 and 43) held together with the lead wires (27) of a vortex detection sensor (11) within the internal space (35), and the lead wires (27, 42, and 43) thus held together are led out toward the flow rate converter (not shown) via a metal pipe (34). Since the lead wires (27, 42, and 43) are held together within the internal space (35) and led out toward the flow rate converter via the metal pipe (34), there is involved only one joint portion between the sensors and the flow rate converter. With this structure, explosion-proof performance can be attained easily.