Liquid medicine injection device, drug injection device, and method for determining remaining amount of drug thereof

A medical liquid injection device comprising:

• a base body;
• a needle assembly mounted on the base body;
• a reservoir fluidly connected to the needle assembly and having an inner space in which a medical liquid is stored;
• a plunger disposed inside the reservoir, and configured to move in a longitudinal direction of the reservoir according to an amount of the medical liquid stored in the reservoir;
• and
• a first sensor unit configured to measure the amount of the medical liquid stored in the reservoir according to the movement of the plunger,
• wherein the plunger includes a connector member mounted on one side thereof and extending in the longitudinal direction of the reservoir, and
• wherein the first sensor unit includes a plurality of contact terminals disposed on a movement path of the connector member,
• wherein the connector member is brought into contact with the contact terminals according to the movement of the plunger to sense the amount of the medical liquid stored in the reservoir based on a moving distance of the plunger.