A heater chip (4) as a heat generation element is secured to the surface on the periphery of piping (2). Further, a temperature sensor chip couple (6) is placed on the surface on the periphery of the piping (2), along the direction of flow of fluid flowing in the piping (2). One (6a) of the sensor chips in the couple is placed on the upstream side of the heater chip (4) and the other (6b) is placed on the downstream side of the heater chip (4). The heater chip (4) and the temperature sensor chips (6a, 6b) are formed in a chip type. The temperature sensor chips (6a, 6b) as the pair are placed at positions spaced by the same distance from the heater chip (4).