To provide a leg structure of a mounting member for mounting a member to be mounted to a panel hole of a counterpart panel, allowing small insertion force and large extraction force by providing a thick shaft part and a thin shaft part on a pin member and providing a biasing tool between the same and a grommet member.

The leg structure includes, between the pin member 50 and the grommet member 40, the biasing tool (for instance a spring 101) for biasing them in directions separating from each other and for positioning the thick shaft part 112 inside of an elastic leg 72. When inserting the pin member 50, by pushing the same in the insertion direction against the biasing tool (for instance the spring 101), the thin shaft part 113 is positioned inside of the elastic leg 72 to allow the elastic leg 72 to bend toward a hollow interior of the elastic leg 72. Then, the pin member 50 is returned by the biasing force of the biasing tool (for instance the spring 101) to position the thick shaft part 112 inside of the elastic leg 72.