FLOW MEASURING DEVICE

PROBLEM TO BE SOLVED: To dispense with installation of a weir and to prevent a foreign substance from accumulating by detecting water pressure at a high pressure side pressure receiving part provided facing to the upstream direction and a low pressure side pressure receiving part provided facing to the downstream direction, and obtaining a flow rate based on the differential pressure, and flow speed and water level computed from the static pressure at the same point. SOLUTION: A differential pressure detector 1 is constituted by arranging two water pressure detecting elements on the surface and back in parallel, one detecting element is faced to the upstream direction as a high pressure side pressure receiving part 2, the other is faced to the downstream direction as a low pressure side pressure receiving part 3, and the respective ones are vertically installed on the bottom of the water passage. Both pressure receiving parts 2, 3 detect water pressures, and the differential pressure signals is applied to a converter 5 through a cable 4. At this time the detector 1 detects static pressure of the provided position by a static pressure sensor 1a to send to the converter 5. The converter 5 computes flow speed and water level up to the water surface from the differential pressure signal and the static pressure signal, and further computes the flow based on the water level, the flow speed, and the breadth of a water passage.