PURPOSE: To automate fitting of a push-fit part by pushing the push-fit part such as a grommet, etc., a fitting hole by means of a position-displacing device control means for returning a holding device to its original position and a displacement measuring means for measuring the displacement of the holding device.

CONSTITUTION: Regardless of the actual relative positions of a robot 6 and a body panel 28, a grommet 20 held by a holding device situated at an indexed position of eight holding devices of handle 22 is first positioned by a controller 8 so that it stands just opposite a fitting hole 30 of the body panel 28, and then based on the results of photographing the body panel 28 by a TV camera 204, the position of the handle 22 is corrected so that the grommet 20 stands just opposite to the fitting hole 30, in consideration of the actual relative positions of the grommet 20 and the fitting hole 30. Thereafter, the grommet 20 is pushed and fitted into the fitting hole 30 by an air cylinder. Thus, fitting of the grommet 20 to the body panel 28 is automatically performed.