A dishwasher comprising: a washing tub for accommodating washing targets; a spray arm rotatably provided in the washing tub, for spraying washing water toward the washing targets; and a spray arm holder provided with a channel for supplying washing water to the spray arm, wherein the spray arm includes: a body having a plurality of channels through which washing water moves by being partitioned, and a plurality of spray holes for discharging washing water entering each channel toward the washing targets; a chamber provided at a lower portion of the body and communicated with the plurality of channels; a channel guider for supplying the washing water flowing from the spray arm holder to the chamber, wherein the channel guider is coupled to the spray arm holder by passing through the body and the chamber, and rotatably supports the body and the chamber, wherein the channel guider includes a guider body for supporting the chamber and the body at a lower portion of the chamber; and a channel switch unit accommodated in the chamber, alternately opening and closing the plurality of channels (731, 733), wherein the plurality of channels include a first channel for supplying washing water to a first spray hole for rotating the body in a first direction, and a second channel for supplying washing water to a second spray hole for rotating the body in a second direction, and the body includes a first chamber communication hole for communicating the first channel with the chamber, and a second chamber communication hole for communicating the second channel with the chamber, and the channel switch unit alternately opens the first chamber communication hole and the second chamber communication hole. a washing tub for accommodating washing targets; a spray arm rotatably provided in the washing tub, for spraying washing water toward the washing targets; and a spray arm holder provided with a channel for supplying washing water to the spray arm, wherein the spray arm includes: a body having a plurality of channels through which washing water moves by being partitioned, and a plurality of spray holes for discharging washing water entering each channel toward the washing targets; a chamber provided at a lower portion of the body and communicated with the plurality of channels; a channel guider for supplying the washing water flowing from the spray arm holder to the chamber, wherein the channel guider is coupled to the spray arm holder by passing through the body and the chamber, and rotatably supports the body and the chamber, wherein the channel guider includes a guider body for supporting the chamber and the body at a lower portion of the chamber; and a channel switch unit accommodated in the chamber, alternately opening and closing the plurality of channels (731, 733), wherein the plurality of channels include a first channel for supplying washing water to a first spray hole for rotating the body in a first direction, and a second channel for supplying washing water to a second spray hole for rotating the body in a second direction, and the body includes a first chamber communication hole for communicating the first channel with the chamber, and a second chamber communication hole for communicating the second channel with the chamber, and the channel switch unit alternately opens the first chamber communication hole and the second chamber communication hole. a body having a plurality of channels through which washing water moves by being partitioned, and a plurality of spray holes for discharging washing water entering each channel toward the washing targets; a chamber provided at a lower portion of the body and communicated with the plurality of channels; a channel guider for supplying the washing water flowing from the spray arm holder to the chamber, wherein the channel guider is coupled to the spray arm holder by passing through the body and the chamber, and rotatably supports the body and the chamber, wherein the channel guider includes a guider body for supporting the chamber and the body at a lower portion of the chamber; and a channel switch unit accommodated in the chamber, alternately opening and closing the plurality of channels (731, 733), wherein the plurality of channels include a first channel for supplying washing water to a first spray hole for rotating the body in a first direction, and a second channel for supplying washing water to a second spray hole for rotating the body in a second direction, and the body includes a first chamber communication hole for communicating the first channel with the chamber, and a second chamber communication hole for communicating the second channel with the chamber, and the channel switch unit alternately opens the first chamber communication hole and the second chamber communication hole.