An intravenous catheter inserting device includes a catheter hub engaging an open forward end of a barrel and having a duct that communicates with a passage of the barrel. A tubular catheter is disposed to communicate with the duct, and permits a needle cannula to pass therethrough. A plunger is received in the passage and extends rearwardly of the barrel so as to be manually operable. The plunger has a cavity containing fluid at a reduced pressure, and is coupled with the needle cannula within the passage such that the needle cannula can be retracted into the cavity due to a pressure difference between the ambient air and the reduced pressure.