To provide a sealing method for a cylindrical member to be set at an opening of a pipe, capable of constructing a sealing structure in the cylindrical member in a short period of time even when many cables extending from monitor elements arranged inside the pipe are inserted into the cylindrical member, and to provide a closing method for the pipe, a sealing structure of the cylindrical member, and a closing structure of the pipe, by using the cylindrical member.

A sealing method for a metallic cylindrical member 22 where cables are inserted is characterized in that: a partition plate 26 divides an internal space 28 of the cylindrical member 22; cables 20 are inserted through the partition plate 26 so as to be inserted into the cylindrical member 22; and a heat-generating adhesive (a heat-generating adhesive layer 34) is filled at one surface side (an internal space 30) of the partition plate 26 in the internal space 28 so as to seal the one surface side, and a thermosetting adhesive (a thermosetting adhesive layer 36) is filled at the other surface side (an internal space 32) of the partition plate 26 in the internal space 28 so as to seal the cylindrical member 22 by curing the thermosetting adhesive by heat generated by the heat-generating adhesive.