A vacuum sealing structure (1) for connecting a first connection part (13) with a second connection part (43) via a gasket (31). The first connection part (13) or the second connection part (43) is provided with a jaw (43a), having an end portion which is broadened outwardly of a pipe member forming a vacuum passage, and a support member (21) having an annular tapered groove (21a). The second connection part (43a) directly contacts the gasket (31) and a tapered groove (21a). Thus the second connection part tapered jaw (43a) is tightly pressed against the gasket (31) by fastening the support member (21) with a fastening member (15), thereby achieving a vacuum sealing structure for facilitating the sealing of a body (2) to be vacuum sealed. The body may be a viewing port (41). Since it is not necessary to secure the body (2) to a flange (21), welding for securing will not be required and no trouble will be caused with sealing. In the event that the body (2) is damaged, all that is required is to replace the body itself, enabling easy maintenance.