A dishwasher comprising: a tub having a space for accommodating an object to the washed; and a spray arm comprising a pair of main arms provided in the tub and extending in one direction for spraying wash water to the object, and a pair of auxiliary arms (140, 150) extending in another direction while being spaced apart from the main arms by a predetermined angle for spraying wash water to the object, wherein the dishwasher further comprises: an arm holder detachably disposed in the tub, the arm holder defining a channel through which wash water moves to the spray arm, wherein the arm holder is configured for supporting the spray arm so as to be rotated in a floating state in accordance with spraying of wash water from the main arms and the auxiliary arms (140, 150); and a flow passage switching unit, provided inside the arm holder; said dishwasher being characterized in that the pair of auxiliary arms (140, 150) rotate about a rotation axis defined by a direction in which the auxiliary arms (140, 150) extend; and in that said flow passage switching unit is provided to be vertically movable, for selectively supplying wash water to the main arms or the auxiliary arms (140, 150) in accordance with supply and interruption of wash water. a tub having a space for accommodating an object to the washed; and a spray arm comprising a pair of main arms provided in the tub and extending in one direction for spraying wash water to the object, and a pair of auxiliary arms (140, 150) extending in another direction while being spaced apart from the main arms by a predetermined angle for spraying wash water to the object, wherein the dishwasher further comprises: an arm holder detachably disposed in the tub, the arm holder defining a channel through which wash water moves to the spray arm, wherein the arm holder is configured for supporting the spray arm so as to be rotated in a floating state in accordance with spraying of wash water from the main arms and the auxiliary arms (140, 150); and a flow passage switching unit, provided inside the arm holder; said dishwasher being characterized in that the pair of auxiliary arms (140, 150) rotate about a rotation axis defined by a direction in which the auxiliary arms (140, 150) extend; and in that said flow passage switching unit is provided to be vertically movable, for selectively supplying wash water to the main arms or the auxiliary arms (140, 150) in accordance with supply and interruption of wash water. an arm holder detachably disposed in the tub, the arm holder defining a channel through which wash water moves to the spray arm, wherein the arm holder is configured for supporting the spray arm so as to be rotated in a floating state in accordance with spraying of wash water from the main arms and the auxiliary arms (140, 150); and a flow passage switching unit, provided inside the arm holder; said dishwasher being characterized in that the pair of auxiliary arms (140, 150) rotate about a rotation axis defined by a direction in which the auxiliary arms (140, 150) extend; and in that said flow passage switching unit is provided to be vertically movable, for selectively supplying wash water to the main arms or the auxiliary arms (140, 150) in accordance with supply and interruption of wash water.