Disclosed is a plastic cap useful for steadfastly maintaining a sealed state created in a container having a mouth with an opening defined therein by sealing the opening with a sealing member. The plastic cap has a cap main body (1) and a cover portion (2) integrated with the main body via bridge portions (3 see FIG. 1 ). The bridge portions (3) are formed of a synthetic plastic (132) filled in fusion-bonding holes (13) having a diameter of from 0.3 to 3 mm and arranged extending through a top wall (16) of the cap main body (1). The bridge portions (3) are constructed such that the cap main body (1) and the cover portion (2) are integrally fusion-bonded by the bridge portions (3) and the cover portion (2) can be separated from the cap main body (1) by breaking the bridge portions (3) with hands.
