A front-loading-type washing machine comprising: a water tub configured to rotatably support a rotary drum; a detergent supply device configured to supply washing water containing detergents into the water tub; a first water supply valve configured to supply the washing water to the detergent supply device; a water supply connecting pipe configured to connect the water tub and the detergent supply device and is equipped with a backflow preventing portion; a water tub air vent pipe configured to connect the water tub and the detergent supply device; and a control device configured to control at least steps of washing, rinsing, and spin-drying, wherein the detergent supply device has a first water supply passage configured to guide the washing water from the first water supply valve, and a water tub air vent connecting portion connected to the water tub air vent pipe, and wherein the first water supply passage and the water tub air vent connecting portion are configured to communicate with each other; characterized in that: the first water supply passage is configured to provide washing water to a first passage and a second passage which are formed with a number of water pouring ports through which the water falls and is supplied to the water tub via the water supply connecting pipe, wherein a portion of the washing water which has flowed into the first passage reaches the water tub air vent connecting portion and flows into the water tub air vent pipe to be supplied into water tub. a water tub configured to rotatably support a rotary drum; a detergent supply device configured to supply washing water containing detergents into the water tub; a first water supply valve configured to supply the washing water to the detergent supply device; a water supply connecting pipe configured to connect the water tub and the detergent supply device and is equipped with a backflow preventing portion; a water tub air vent pipe configured to connect the water tub and the detergent supply device; and a control device configured to control at least steps of washing, rinsing, and spin-drying, wherein the detergent supply device has a first water supply passage configured to guide the washing water from the first water supply valve, and a water tub air vent connecting portion connected to the water tub air vent pipe, and wherein the first water supply passage and the water tub air vent connecting portion are configured to communicate with each other; characterized in that: the first water supply passage is configured to provide washing water to a first passage and a second passage which are formed with a number of water pouring ports through which the water falls and is supplied to the water tub via the water supply connecting pipe, wherein a portion of the washing water which has flowed into the first passage reaches the water tub air vent connecting portion and flows into the water tub air vent pipe to be supplied into water tub. the first water supply passage is configured to provide washing water to a first passage and a second passage which are formed with a number of water pouring ports through which the water falls and is supplied to the water tub via the water supply connecting pipe, wherein a portion of the washing water which has flowed into the first passage reaches the water tub air vent connecting portion and flows into the water tub air vent pipe to be supplied into water tub.