To provide a fastening device for fastening two structural members to each other into a sealed condition with single operation, and to provide its fastening method.

The fastening device comprises one structural member on the outer periphery of which a sectionally raised portion having a predetermined lead angle is provided, and the other structural member on the inner periphery of which a sectionally raised portion having the same lead angle as the sectionally raised portion of one structural member is provided. On either the outer periphery of one structural member or the inner periphery of the other structural member, the other sectionally raised portion having a lead angle different from the lead angle of the sectionally raised portion thereof is provided. The sectionally raised portion of one of the structural members having the predetermined lead angle is pressed between the sectionally raised portion having the same lead angle and the sectionally raised portion having the different lead angle, and concurrently screwed and moved therein in friction engagement, whereby one structural member is pressed against the other structural member and both structural members are integrally fixed together into the sealed condition.