A rubber plug (1) for a vial container (2) containing medicinal chemicals according to the present invention can be smoothly conveyed by a part feeder while preventing each others adhesion.The top surface of a discoid cap portion (1A) has Shore A hardness of 25 -55 and surface roughness Ra of 2.5 -10.5µ m. Adherence of the top surface of the discoid cap portion (1A) is reduced by synergy effect. The rubber plug (1) can be smoothly conveyed by a part feeder in an inverted position which turns the top surface of the discoid cap portion (1A) to the conveying surface.
