To provide a temperature measuring instrument capable of measuring an average temperature of a fluid at a low cost, a flow meter having the same, and a temperature measuring method.

A flow meter 10 includes a cylindrical measurement pipe 11 connected to the middle of a pipe 80. A flow rate measuring part 14 measures a flow rate of a fluid in the measurement pipe 11. A temperature sensor 20 and a pressure sensor 32 measure temperature and pressure of the fluid in the measurement pipe 11. The temperature sensor 20 is disposed so as to measure the temperature of the fluid at a position separated from the central axis of the measurement pipe 11 by r/√2 when the inner diameter of the measurement pipe 11 is 2r.