Flow measuring device

A flow measuring device comprising:

• a housing defining a passage therein and including a passage narrowing part, which reduces a cross-sectional area of the passage, in a predetermined part of the passage;
• a support having a platy shape and disposed along a flow direction of fluid flowing in the passage;
• and
• a flow measurement element which is located inside the passage narrowing part and disposed on a surface of the support, the flow measurement element being configured to detect a flow rate of fluid flowing in the passage, wherein the passage narrowing part has an inner wall surface that gradually reduces a width of the passage in one of:
• a direction from a center side to an end side of the passage along a height direction of the passage, which is perpendicular to a direction of the width of the passage;
• and
• a direction from one end side to the other end side of the passage along the height direction of the passage.