A washing machine may include a washing tub that is capable of improving washing effect. The washing machine includes: a casing; a washing tub installed in the casing; a plurality of concave sides formed to be recessed into an inner side surface of the washing tub; and a plurality of protrusions that protrude in an inward direction of the washing tub and include a plurality of first protrusions formed on the plurality of concave sides. A frictional force with laundry is generated using a washing tub including the plurality of protrusions and the plurality of concave sides so that a washing force can be enhanced and a flow of washing water can be guided.
