A power seat sliding apparatus is provided which has a superior noise suppression effect and temperature increase suppression effect in a gear mechanism. The gear mechanism 30 is provided with a case310 which pivotably supports a worm 320 and a worm wheel 330, and the case 310 is suspended from and supported by an upper rail 12. The worm 320 is linked to and supported by a rotational force transmitting shaft 220 of a drive mechanism 20, and the worm wheel 330 is screwed onto and supported by a slide screw 11a provided on the lower rail 11. Further, the case 310 is supported on the lower rail11 via a ball 340 as a rolling member. By this means, sliding operations of the case 310 itself are stable, and it is possible to better achieve the noise suppression effect.