The utility model relates to a drum washing machine, which has a structure that air bubble can not attach on a back panel of a perspective window. The drum washing machine comprises a washing house having a washings input/output mouth; a washing door engaged with the washings input/output mouth and having a transparent portion through which view the inner; a water channel elastically supported on the inner of the washing house and having a mouth portion opened in front; a drum installing at the inner of the water channel for receiving washings and being rotatably driven; a water supply element for supplying water to the water channel; and an auxiliary water supply element for supplying water to the water channel in front thereof. Therefore, the air bubble can be removed from the back panel of the perspective window.