A dishwasher comprising: a tub configured to provide a space in which washing objects are held; a spray arm comprising a plurality of channels through which washing water flows, respectively, and spray holes configured to spray the washing water supplied to the channels toward the washing objects; a chamber configured to communicate with the plurality of the channels; a washing water storage portion provided as a partition wall projected at a preset height from a bottom surface of the chamber and comprising a storage space in which the washing water is stored for a preset time period; a path guide penetrating the spray arm, one end of the path guide being provided in the chamber; a washing water supply unit (18, 23) configured to supply the washing water to the chamber through the path guide; a path change unit rotatably provided in the chamber, wherein the path change unit comprises: a path change unit body rotatable at a preset angle by the pressure of the washing water supplied to the chamber; a channel opening hole configured to open some of the channels according to the rotation of the path change unit body; characterized in that the dishwasher further comprises: a buoyancy generating portion provided adjacent to the channel opening hole and configured to raise or lower the path change unit body when provided with the buoyancy by the washing water stored in the washing water storage portion; and upper projections projected from tops of the buoyancy generating portion and the channel opening holes, respectively, to slidingly engage with an upper engaging portion formed in a lower portion of the spray arm. a tub configured to provide a space in which washing objects are held; a spray arm comprising a plurality of channels through which washing water flows, respectively, and spray holes configured to spray the washing water supplied to the channels toward the washing objects; a chamber configured to communicate with the plurality of the channels; a washing water storage portion provided as a partition wall projected at a preset height from a bottom surface of the chamber and comprising a storage space in which the washing water is stored for a preset time period; a path guide penetrating the spray arm, one end of the path guide being provided in the chamber; a washing water supply unit (18, 23) configured to supply the washing water to the chamber through the path guide; a path change unit rotatably provided in the chamber, wherein the path change unit comprises: a path change unit body rotatable at a preset angle by the pressure of the washing water supplied to the chamber; a channel opening hole configured to open some of the channels according to the rotation of the path change unit body; characterized in that the dishwasher further comprises: a buoyancy generating portion provided adjacent to the channel opening hole and configured to raise or lower the path change unit body when provided with the buoyancy by the washing water stored in the washing water storage portion; and upper projections projected from tops of the buoyancy generating portion and the channel opening holes, respectively, to slidingly engage with an upper engaging portion formed in a lower portion of the spray arm. a path change unit body rotatable at a preset angle by the pressure of the washing water supplied to the chamber; a channel opening hole configured to open some of the channels according to the rotation of the path change unit body; characterized in that the dishwasher further comprises: a buoyancy generating portion provided adjacent to the channel opening hole and configured to raise or lower the path change unit body when provided with the buoyancy by the washing water stored in the washing water storage portion; and upper projections projected from tops of the buoyancy generating portion and the channel opening holes, respectively, to slidingly engage with an upper engaging portion formed in a lower portion of the spray arm. a buoyancy generating portion provided adjacent to the channel opening hole and configured to raise or lower the path change unit body when provided with the buoyancy by the washing water stored in the washing water storage portion; and upper projections projected from tops of the buoyancy generating portion and the channel opening holes, respectively, to slidingly engage with an upper engaging portion formed in a lower portion of the spray arm.