To provide a flow rate measuring unit for precisely measuring a flow rate regardless of the mounting position to piping.

A plurality of analysis data by a three-dimensional numeric analysis with a flow rate, where an upstream side piping system is converted into a numeric model, as a parameter are stored at a data storage section 11 as a database, and a measurement computing means 13 calculates the time average value of a plurality of measurement data in the upstream side piping system for computing the average value and standard deviation of the time-averaged measurement data group. A data comparison processing means 15 selects analysis data, where the average value and standard deviation of the measurement data group time-averaged by the measurement computing means 13 statically agree, in analysis data fetched by a data taking-out means 14. A flow rate correction coefficient calculation means 16 calculates the flow rate correction coefficient of a measurement system, based on the analysis data selected by the data comparison processing means 15.