An administering instrument is disclosed, which is capable of preventing a needle tube from coming out of a living body during administration of a drug solution and a drug solution administering system including the administering instrument and a medicinal solution administering device. The administering instrument includes a puncture part that has a contact surface contacting a body surface H of a user, a needle holding part for holding a needle tube, and a communication passage communicating with a lumen of the needle tube. The puncture part includes a fixing part that is disposed above the contact surface and fixes the first end part of the tube to the puncture part in a state where the first end part of the tube is inclined toward the contact surface of the puncture part.