To insertionally mount a grommet correctly and quickly into the hole part or recess of a pallet by arranging a grip device, for gripping a grommet housing member for housing a placing hammer device and many grommets in a placing robot.

The lower opening of a grommet housing member 5a, gripped by the gripping member 111 of a grip device 14, is arranged directly on the recess p1 of a pallet P. A grommet G, housed between upper and lower partitioning plates, is placed on the recess p1 of the pallet P. Then, a placing robot is adequately controlled, to insertionally mount the grommet G into the recess p1 of the pallet P, by the hammer 13' of a placing hammer device 13.