To easily check and replace a sprinkler head by employing structure such that a sprinkler head is easily and surely fitted to an exact position so as to avoid water leakage and can be removed.

Between a joint 10 and a fitting part of the sprinkler head S, an O-ring 30 being a seal member for holding water-tightness in contact with both thereof is provided. At the inner periphery of the joint 10, a lock ring 20 having spring property is provided in a diametrically expandable manner. At the outer periphery of the fitting part 1 of the sprinkler head S, a step part 7 to which the lock ring 20 is fitted is disposed. At the step part 7, a tilting guide surface 6 for guiding the lock ring 20 is provided. Thus, at the thread terminating position of the sprinkler head S, the lock ring 20 is fitted into the step part, so that the sprinkler head S can be joined to the joint 10.