A shock absorbing damper incorporated into a shock absorbing/door pull-in mechanism includes a piston inside thereof. If the sliding door is moved in a closing direction, one end of a rod connected to the sliding door closes a pressure release hole formed in a central portion of the piston. Then, a resistance to movement of the piston is generated to absorb a shock occurring when the sliding door is closed. On the other hand, if the sliding door is moved in an opening direction, the rod is separated from the piston. As a result, the pressure release hole in the piston is opened and a shock attenuating medium (oil) flows through the pressure release hole and therefore the sliding door moves lightly.