PROBLEM TO BE SOLVED: To provide an indwelling needle which can connect a catheter to a medical extracorporeal circuit while excluding air bubbles with a simple operation.SOLUTION: An indwelling needle introduced into a blood vessel and used for connection to a medical extracorporeal circuit, comprises: a catheter in fluid communication with the blood vessel a connector which is connected to the catheter so as to be in fluid communication with the interior of the catheter, and is used for connection to the extracorporeal circuit a valve which is fitted with the connector in a fluid-tight manner while being restricted from moving forward, and is closed a plug stored in the connector so as to push and open the valve when moving forward an elastic body for energizing the plug in a backward direction a passage for gas-communicating the interior and exterior of the catheter and a needle which passes through the valve pushed and opened by the plug and penetrates the catheter removably, and guides the catheter into the blood vessel by puncture.
