FLOW RATE MEASURING DEVICE

Provided is a flow rate measuring device including a connector portion, a main body portion, an internal flow passage, and a flow rate detection element. The internal flow passage includes a main flow passage and a sub-flow passage. The sub-flow passage includes a flow rate detection element-side flow passage and connection flow passages. The main flow passage includes an introduction portion, a small flow passage sectional area portion, and an exit portion. The connection flow passages include an upstream-side connection flow passage and a downstream-side connection flow passage. The main flow passage and the flow rate detection element-side flow passage are formed so as to be symmetric with respect to a plane having a flow direction of the fluid to be measured flowing through the pipe as a normal. The main flow passage has a portion at the plane of symmetry as the small flow passage sectional area portion.