PROBLEM TO BE SOLVED: To assemble a safety needle with high productivity without damaging a flexible sleeve.SOLUTION: An assembly method of a safety needle engages a cover 5 with a needle or a guide pin 25, presses the cover 5 and the needle or guide pin 25 against a film 11 stretched in parallel to the needle or the guide pin 25, adheres the film 11 in the way that the needle or the guide pin 25 is encircled to form a film tube, separates the film tube from the film 11 to form a sleeve at the same time or after adhering the film 11 to form a sleeve, joins the sleeve to the cover 5, inserts the sleeve joined to the cover 5 and the needle into the handle, and adheres the sleeve to the handle.