PURPOSE: To prevent a dead volume, to enable the execution of accurate analysis, and to enable the attainment of a prescribed sealing pressure even by an operation with a relatively small force, by pressing the flat-surface portion of the end of a tube on a seal seat surface formed around a channel.

CONSTITUTION: By holding the head of a push bolt 31 on its side between fingers and tightening it, the end portion of the push bolt 31 is made to contact with a ferrule 34 fixed to a tube 33, and thereby the tube 33 is made to advance into a connection port section 36. Then, first the end portion of the tube 33 gets into the cavity 37a of a cylindrical packing 37 and, with a further advance, a flat- surface portion 33a of the end of the tube 33 comes into contact under pressure with the seal seat surface 37c of the cylindrical packing 37, and thus sealing is made by the flat-surface portion 33a of the end of the tube 33. Moreover, the cylindrical packing 37 is in close contact under pressure with the bottom surface 36c of the connection port section 36 and further is deformed in an inflating manner, and consequently the inside surface of the connectio port section 36 and the outer peripheral surface of the end portion of the tube 33 are also connected liquid-tightly with each other.