Abstract: A regulator for regulating a flow rate is provided with an upper connector having a downwardly opened channel in communication with the regulator. An on-off valve connected to the regulator is provided with a lower connector having an upwardly opened channel in communication with the on-off valve. The upper connector is lapped over the lower connector and removably joined thereto with a screw so as to cause the downwardly opened channel to communicate with the upwardly opened channel. Accordingly, the regulator can be removed singly, for example, when malfunctioning.