A syringe assembly (10) of the present invention is composed of an outer cylinder (2) and a seal cap (3). The outer cylinder (2) has an outer cylinder body part (21), a piercing needle mounting part (22), and a piercing needle (6) fixed to the piercing needle mounting part. The seal cap (3) has a closed distal end part (31), an open proximal end part (32), a piercing needle mounting part-accommodating part (35) accommodating a distal end portion of the piercing needle mounting part, a piercing needle accommodating part (34), and a pierceable part (33) into which the piercing needle tip is pierceable. A polyparaxylylene coating is provided on an inner surface of the piercing needle mounting part-accommodating part of the seal cap or on an outer surface of the piercing needle mounting part of the outer cylinder. The inner surface of the piercing needle mounting part-accommodating part of the seal cap and the outer surface of the piercing needle mounting part of the outer cylinder are kept in close contact with each other through the polyparaxylylene coating.
