PROBLEM TO BE SOLVED: To abolish an operation for screwing fine components for connection of channels of an oxygen concentrator miniaturized to be turned into a portable type.SOLUTION: In a method for fixing a cylindrical unit, a manifold molding with a built-in channel for forming a process, and the cylindrical unit are seal-fitted together by inserting a joint, which is provided at an end part of the cylindrical unit, into a fitting part, which is provided in the manifold molding, via an O-ring provided on the outer periphery of the joint part, and an outer peripheral part of the manifold molding and a groove provided on the outer periphery of the joint part are fixed by being pinched by a clip member comprising a U-shaped part for being fitted into the groove.
