To provide a seal device that has high hermeticity even under high hydraulic pressure.

A plurality of gaskets are arranged zigzag, and each comprise a gasket body which is an elastic body and a gasket case. The packaging case includes a case back part which covers the back of the gasket body and a case side face part covering at least one of right and left side faces of the gasket body on the side face. A case projection part which projects forward from a front end of the packing body is provided at a fronto end of the case side face part, and while a case projection part of one gasket abuts against a gasket body of the other opposite gasket, a case projection part of the other gasket abuts against the gasket body of the one gasket.