To fit a grommet in a through hole by eliminating insertion resistance.

The grommet 10 is constituted of a large-diameter cylindrical outer body 11 in which a resin-made ring-like inner body 13 is put and which is made of rubber or elastomer, and a small-diameter cylindrical outer body 12 into which a resin-made cylindrical inner body 14 is put and which is made of rubber or elastomer. Locking pieces 13c are protruded in the axial direction from the ring-like inner body 13 while the pieces 13c are inclined in radial reducing directions. The cylindrical outer bodies 11 and 12 are connected to each other by passing the pipe section 14b of the cylindrical inner body 14 through the body 12. Then the grommet 10 is fitted to the through hole Pa by pushing the pipe section 14b into the hole Pa after the locking pieces 13c are passed through the hole Pa and pushing out the pieces 13c.