Injection device

A metered dosing component comprising;

• a plunger having a protruding portion on an outer surface thereof,
• a flange cover to be placed over a flange portion of a syringe, having a hole through which the plunger passes, and a recess provided in an inner surface of the hole through which the protruding portion passes, wherein
• the protruding portion has a first protruding portion extending axially to a front end side of the plunger, a second protruding portion extending axially to a rear end side of the plunger and located at a different position from the first protruding portion in the circumferential direction, and a continuous protruding portion connecting a rear end of the first protruding portion and a front end of the second protruding portion in a continuous manner,
• when the flange cover is attached to the flange portion of the syringe and the plunger is inserted into the syringe, and the plunger is pulled backward from a position where the second protruding portion is located in the recess, the second protruding portion, the continuous protruding portion, and the first protruding portion pass through the recess in that order, and when the rear end of the first protruding portion passes through the recess, the plunger rotates with respect to the flange cover.