Abstract: In a connection structure of a pipe in which a first pipe provided outside a case and a second pipe provided inside the case are connected via a gasket while sealing a space between the first pipe and a through hole provided on a wall body of the case and a space between the through hole and the second pipe, the gasket has a tubular first holding portion, an inner circumferential first lip portion, an outer circumferential lip portion, a tubular second holding portion, and an inner circumferential second lip portion. Resistance applied on the first holding portion including the inner circumferential first lip portion when the first pipe is pulled out of the through hole is smaller than total of resistance generated in the outer circumferential lip portion against pull-out direction and resistance generated in the inner circumferential second lip portion against pull-out direction.