In a prefilled syringe including an elastic seal member to be pierced with a needle for use to eject a protein pharmaceutical preparation therefrom, the elastic seal member ensures smooth and reliable piercing thereof with the needle while reliably preventing an active substance of the protein pharmaceutical preparation from being adsorbed thereon. When a protective film (3) is laminated to a top surface of a seal body (2) of an elastic material, the protective film (3) is stretched to a greater extent by a recess (4) provided in the top surface. Further, the piercing portion to be pierced with the needle is provided in a bottom of the recess (4). Thus, the protective film (3) is formed as locally having a smaller thickness in the piercing portion.