PROBLEM TO BE SOLVED: To provide a container seal method and a device by which a cut sheet material can be efficiently sealed with by hardly wasteful and simple movement without making the cut sheet material protrude from an outer edge of a container.SOLUTION: In a container seal method, a sheet material 13 is fitted to an opening edge surface 23a of the container 11 by performing a cut step, a retention step, a transfer step and a pressure bonding step. An opening 26 is covered and sealed with the sheet material 13. In the cut step, a sheet material cut piece 13a is cut out by a cutting means 51 having a cutting part 52. In the retention step, a retaining means 61 movable forward and backward through a cut part 52 inner side is used. The retaining means 61 is operated in the forward direction during a cut-out operation and the sheet material cut piece 13a is retained on a top end surface 62. During the transfer step, the retaining means 61 is further operated in the forward direction and the sheet material cut piece 13a is transferred to the opening edge surface 23a. Thereafter, the sheet material cut piece 13a is pressed and bonded.
