To provide a high sealability without deforming a mounted member of low rigidity.

In this gasket mounting structure wherein a gasket 1 is mounted in a state of being held in connecting parts 2a, 3a of two members one of which 3 has the rigidity lower than the other member 2, and a mounting part 5 of the gasket 1 is inserted into a mounting groove 4 formed on the connecting part 3a of the member 3 of two members 2, 3, a radius of curvature of a top part 10 of the mounting part 5 of the gasket 1 is smaller than a radius of curvature of a corner part 13 of a bottom face 11 and a side face 12 of the mounting groove 4.