To simplify the piping work, reduce the cost by decreasing the number of component parts, and increase the degree of freedom in routing of pipes by making the mounting pose adjustable.

In a flow rate sensor containing manifold unit 1, a main pipe 2 and a plurality of branch pipes 3, 3, 3 branched off from the main pipe 2 are integrally formed, and a flow rate sensor 4 for detecting the flow rate of fluid flowing through a channel 31 of each branch pipe 3 is installed in the branch pipe 3. As for a joint between the main pipe 2 and the branch pipe 3, such conventional sealing structure as to use a nipple is not required. Further, a pipe adapter 73 including leg portions 734 is detachably attached to an opening end of the main pipe 2. By changing the direction of the pipe adapter 73 so as to secure the leg portions 734 to an installation surface A, the mounting pose of the manifold unit 1 can be made adjustable.