A coupling comprises a holding member having a U-shaped cross section, and a channel member held by the holding member. The holding member has an upper wall formed with screw bores for use in attaching the holding member to a fluid controller. The channel member comprises a body having an inner channel and fitted in a space between the upper wall of the holding member and a lower wall thereof, a tubular upward projection communicating with the inner channel of the body and having an upper end inserted in a through bore in the upper wall of the holding member to communicate with a downward channel of the fluid controller, and a tubular lateral projection communicating with the inner channel of the body and extending laterally. The upper end of the channel member has an outward flange, and the through bore of the upper wall of the holding member has an inward flange for supporting the flange.