Problems to be solved by the inventionTo provide a connection structure of a connector that can prevent cracks or leakage of liquid.ConstitutionFemale thread (34) formed on the inner peripheral surface of lock ring (28) equipped in male connector (22) and male thread (25) formed on the outer peripheral surface of female connector (21) are screwed to each other so that male connector (22) and female connector (21) are connected to each other. Here, protrusion strips (26a), (26b) are formed on the rear side portion of male thread (25) on the outer peripheral surface of female connector (21), and notches (3 5 a), (35b) that can engage with said protrusion strips (26a), (26b) are set on the tip portion of lock ring (28). As a result, when male thread (25) and female thread (34) are screwed to each other, the screwed state is appropriate when protrusion strips (26a), (26b) and notches (35a), (35b) are engaged with each other.
