To provide a flow cell being employed in an optical measuring system, especially suitable for measurement of liquid food, and a manufacture thereof.

In a flow cell molded integrally with one synthetic resin material, extension members 70, 72 extending oppositely in the radial direction from the inner surface 71 of side wall are provided, on the end face parts thereof, with search window areas 76a, 76b and disposed to allow passage of infrared rays in the direction normal to the axis of a tubular passage 74. Consequently, the flange structure can be eliminated and the number of components of flow cell can be decreased greatly. Furthermore, since no fitting is required for sealing, generation of gap can be prevented efficiently at the border surface between the extension members 70, 72 and the side wall 71.