[Problem] A plug for a container capable of improving air-tightness and liquid-tightness is provided. [Solution] A plug (20) includes a first split piece (29) having a cylindrical first fitting portion (26) to be mounted on an opening portion (33) of a container body (24) and fitted to an opening portion space (25) of the opening portion (33), an end wall (27) which blocks one end of the first fitting portion (26), and a first flange portion (28) extending outwardly in a radial direction of the first fitting portion (26) from the other end thereof; and a second split piece (33) having a second fitting portion (31) which is fitted to the first fitting portion (26) of the first split piece (29) and forms a closed space (30) between the end wall (27) and the second fitting portion (31) and a second flange portion (32) extending outwardly in a radial direction of the second fitting portion (31) therefrom.
