A drug administration instrument including a syringe including: a tubular surrounding periphery portion forming a drug chamber configured to store a drug a discharge part disposed at a first axial end of the surrounding periphery portion and a flange portion disposed at a second axial end of the surrounding periphery portion and a sheath member having a tubular shape, surrounding an outer circumference of the surrounding periphery portion of the syringe, and holding the syringe. The sheath member includes a fitting part configured to support at least one of the surrounding periphery portion and the discharge part of the syringe.
