Provided is an indwelling needle assembly having a novel structure with which a needle tip of an inner needle extracted from an outer needle is covered, enlargement of an outer needle hub to an outer peripheral side can be avoided, and treatment work becomes easier. A connection member 94 extends from a needle tip protector 22 to an inside of an outer needle hub 26 and restricts movement of the outer needle hub 26 relative to the needle tip protector 22 by contact with an inner face of the outer needle hub 26, thereby keeping a connected state by a connection mechanism. A disconnection mechanism is provided which moves the connection member 94 to an inner peripheral side of the outer needle hub 26 when an inner needle 18 is extracted from an outer needle 24, to release the connected state of the outer needle hub 26 to the needle tip protector 22.
