The invention provides a washing machine filtering device disposed on the discharge opening formed on the inner side of the washing tank for filtering the foreign matters contained in water pumped by the revolving force of the washing tank. The filtering device in the washing machine comprises: a cap having multiple spraying holes formed thereon for spraying washing water to the washing tank; a closed type filtering component for filtering the foreign matters combined on the cap in a demountable way; and a mounting-demounting device disposed on the cap for mounting and demounting the filtering device on the discharge opening. The filtering device can filter the foreign matters in the water while washing, and can be mounted to or dismounted from the washing machine easily.