GASKET ASSEMBLING METHOD AND GASKET

In a gasket for sealing a gap between a throttle body and an intake manifold that are assembled obliquely to each other, sealing performance is stabilized by preventing the gasket from falling or being caught. A gasket (1) with a substantially pentagonal cross-section is set in an installation groove (21) before a throttle body (20) and an intake manifold (30) are assembled. The gasket (1) is then brought to be in contact only with a close-contact surface (31) of the intake manifold, to which surface, with a throttle body (20) assembled to an intake manifold (30), the gasket (1) in the installation groove is in close contact. After that the throttle body (20) is assembled to the intake manifold (30) by making the gasket (1) to be in sliding contact with the close-contact surface (31).