PURPOSE: To provide a simple device for absorbing inertia of a sliding door to make quiet the noise at a position just before a side part even if the door is slid with a strong force.

CONSTITUTION: At a lower end of a sliding door 1 a door wheel 3 and a shaft or pin 4 are arranged. At the center of a rail groove 6M of a guide rail 6 supporting the wheel 3 of the door 1, a narrow width part 62 guiding the pin 4 when it is inserted therein is arranged. The bottom groove width of the groove 6M is made larger than the part 62 while a stopper 7 is arranged, the stopper 7 having a cut groove 71 in which the pin f4 can be inserted to absorb the inertia of the door 1.