PURPOSE: An O-ring coupling structure is provided to prevent the separation of O-rings from the coupling grooves of parts although grease is not spread. CONSTITUTION: An O-ring coupling structure places and couples an O-ring(20) on an O-ring placing groove(10) formed in one side of parts. A support groove(11) is formed in one wall of the O-ring placing groove and a protrusion(21) is formed in one side of the O-ring at a position corresponding to the support groove. The support groove and the protrusion are a semi-circular shape.
