Thermal type flow measuring device

A first sub passage portion and a second sub passage portion are configured so as to form layers on both sides of a separation wall, respectively. A linear passage portion of a third sub passage portion is formed so that a cross section thereof extends within a range across both sides of the separation wall in a direction perpendicular to a wall surface of the separation wall. The cross section is taken along a direction perpendicular to a flow direction of a fluid flowing through the linear passage portion. The separation wall separates the layer of the first sub passage portion and the layer of the second sub passage portion from each other. A first communication passage portion which allows the first sub passage portion to communicate with the third sub passage portion curves to make a directional change and connects a passage wall surface of the first sub passage portion to a side wall of the third sub passage portion by an inclined surface. The passage wall surface is defined by the separation wall. The side wall is located on a side of the second sub passage portion with respect to the separation wall. A through passage which passes through the separation wall is provided in a second communication passage portion which allows the second sub passage portion to communicate with the third sub passage portion.